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 $57.31   13.489%   $65.0405   $65.04   $65.05   $65.00  
  Purchase #2 $101.92   8.600%   $110.6851   $110.69   $110.70   $110.70  
  Purchase #3 $87.83   6.652%   $93.6725   $93.67   $93.65   $93.70  
  Purchase #4 $11.63   7.213%   $12.4689   $12.47   $12.45   $12.50  
  Purchase #5 $61.81   4.433%   $64.55   $64.55   $64.55   $64.60  
  Purchase #6 $65.90   3.147%   $67.9739   $67.97   $67.95   $68.00  
  Purchase #7 $68.66   11.552%   $76.5916   $76.59   $76.60   $76.60  
  7 purchase totals = $455.06       $490.9825   $490.98   $490.95   $491.10