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 $54.32   8.570%   $58.9752   $58.98   $59.00   $59.00  
  Purchase #2 $182.40   9.837%   $200.3427   $200.34   $200.35   $200.30  
  Purchase #3 $169.38   9.870%   $186.0978   $186.10   $186.10   $186.10  
  Purchase #4 $102.53   4.448%   $107.0905   $107.09   $107.10   $107.10  
  Purchase #5 $201.73   3.806%   $209.4078   $209.41   $209.40   $209.40  
  Purchase #6 $64.25   9.198%   $70.1597   $70.16   $70.15   $70.20  
  Purchase #7 $160.66   4.387%   $167.7082   $167.71   $167.70   $167.70  
  7 purchase totals = $935.27       $999.7819   $999.79   $999.80   $999.80