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 $60.49   13.155%   $68.4475   $68.45   $68.45   $68.40  
  Purchase #2 $87.82   4.667%   $91.9186   $91.92   $91.90   $91.90  
  Purchase #3 $97.65   3.684%   $101.2474   $101.25   $101.25   $101.20  
  Purchase #4 $230.65   12.121%   $258.6071   $258.61   $258.60   $258.60  
  Purchase #5 $76.53   12.275%   $85.9241   $85.92   $85.90   $85.90  
  Purchase #6 $11.81   13.652%   $13.4223   $13.42   $13.40   $13.40  
  Purchase #7 $95.67   9.580%   $104.8352   $104.84   $104.85   $104.80  
  7 purchase totals = $660.62       $724.4022   $724.41   $724.35   $724.20