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 $52.54   10.756%   $58.1912   $58.19   $58.20   $58.20  
  Purchase #2 $73.56   3.668%   $76.2582   $76.26   $76.25   $76.30  
  Purchase #3 $155.27   7.315%   $166.628   $166.63   $166.65   $166.60  
  Purchase #4 $213.55   7.258%   $229.0495   $229.05   $229.05   $229.00  
  Purchase #5 $235.56   5.470%   $248.4451   $248.45   $248.45   $248.40  
  Purchase #6 $61.29   9.660%   $67.2106   $67.21   $67.20   $67.20  
  Purchase #7 $122.90   13.669%   $139.6992   $139.70   $139.70   $139.70  
  7 purchase totals = $914.67       $985.4818   $985.49   $985.50   $985.40