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 $72.36   5.281%   $76.1813   $76.18   $76.20   $76.20  
  Purchase #2 $65.81   4.310%   $68.6464   $68.65   $68.65   $68.60  
  Purchase #3 $110.65   10.665%   $122.4508   $122.45   $122.45   $122.50  
  Purchase #4 $234.44   9.460%   $256.618   $256.62   $256.60   $256.60  
  Purchase #5 $102.39   10.838%   $113.487   $113.49   $113.50   $113.50  
  Purchase #6 $249.90   3.423%   $258.4541   $258.45   $258.45   $258.50  
  Purchase #7 $126.89   12.661%   $142.9555   $142.96   $142.95   $143.00  
  7 purchase totals = $962.44       $1,038.7931   $1,038.80   $1,038.80   $1,038.90