Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $146.25   8.722%   $159.0059   $159.01   $159.00   $159.00  
  Purchase #2 $200.59   6.507%   $213.6424   $213.64   $213.65   $213.60  
  Purchase #3 $126.90   7.153%   $135.9772   $135.98   $136.00   $136.00  
  Purchase #4 $196.43   5.636%   $207.5008   $207.50   $207.50   $207.50  
  Purchase #5 $245.54   7.668%   $264.368   $264.37   $264.35   $264.40  
  Purchase #6 $44.25   11.517%   $49.3463   $49.35   $49.35   $49.30  
  Purchase #7 $158.42   10.487%   $175.0335   $175.03   $175.05   $175.00  
  7 purchase totals = $1,118.38       $1,204.8741   $1,204.88   $1,204.90   $1,204.80