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 $61.44   11.242%   $68.3471   $68.35   $68.35   $68.30  
  Purchase #2 $105.55   7.279%   $113.233   $113.23   $113.25   $113.20  
  Purchase #3 $111.79   13.273%   $126.6279   $126.63   $126.65   $126.60  
  Purchase #4 $93.48   7.579%   $100.5648   $100.56   $100.55   $100.60  
  Purchase #5 $143.97   13.632%   $163.596   $163.60   $163.60   $163.60  
  Purchase #6 $60.96   8.498%   $66.1404   $66.14   $66.15   $66.10  
  Purchase #7 $81.97   4.443%   $85.6119   $85.61   $85.60   $85.60  
  7 purchase totals = $659.16       $724.1211   $724.12   $724.15   $724.00