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 $71.83   5.386%   $75.6988   $75.70   $75.70   $75.70  
  Purchase #2 $215.97   5.738%   $228.3624   $228.36   $228.35   $228.40  
  Purchase #3 $54.67   7.808%   $58.9386   $58.94   $58.95   $58.90  
  Purchase #4 $95.68   9.312%   $104.5897   $104.59   $104.60   $104.60  
  Purchase #5 $163.25   3.238%   $168.536   $168.54   $168.55   $168.50  
  Purchase #6 $70.57   4.398%   $73.6737   $73.67   $73.65   $73.70  
  Purchase #7 $47.74   13.353%   $54.1147   $54.11   $54.10   $54.10  
  7 purchase totals = $719.71       $763.9139   $763.91   $763.90   $763.90