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 $87.54   11.116%   $97.2709   $97.27   $97.25   $97.30  
  Purchase #2 $113.71   11.429%   $126.7059   $126.71   $126.70   $126.70  
  Purchase #3 $54.56   8.465%   $59.1785   $59.18   $59.20   $59.20  
  Purchase #4 $88.27   5.261%   $92.9139   $92.91   $92.90   $92.90  
  Purchase #5 $124.56   4.415%   $130.0593   $130.06   $130.05   $130.10  
  Purchase #6 $54.49   7.504%   $58.5789   $58.58   $58.60   $58.60  
  Purchase #7 $23.26   9.651%   $25.5048   $25.50   $25.50   $25.50  
  7 purchase totals = $546.39       $590.2122   $590.21   $590.20   $590.30