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 $175.46   11.496%   $195.6309   $195.63   $195.65   $195.60  
  Purchase #2 $76.72   8.510%   $83.2489   $83.25   $83.25   $83.20  
  Purchase #3 $219.41   7.223%   $235.258   $235.26   $235.25   $235.30  
  Purchase #4 $68.71   13.147%   $77.7433   $77.74   $77.75   $77.70  
  Purchase #5 $10.38   5.837%   $10.9859   $10.99   $11.00   $11.00  
  Purchase #6 $108.95   11.796%   $121.8017   $121.80   $121.80   $121.80  
  Purchase #7 $216.53   13.403%   $245.5515   $245.55   $245.55   $245.60  
  7 purchase totals = $876.16       $970.2202   $970.22   $970.25   $970.20