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 $48.35   11.117%   $53.7251   $53.73   $53.75   $53.70  
  Purchase #2 $217.94   12.616%   $245.4353   $245.44   $245.45   $245.40  
  Purchase #3 $110.56   7.713%   $119.0875   $119.09   $119.10   $119.10  
  Purchase #4 $191.83   7.648%   $206.5012   $206.50   $206.50   $206.50  
  Purchase #5 $42.46   12.746%   $47.872   $47.87   $47.85   $47.90  
  Purchase #6 $231.39   9.441%   $253.2355   $253.24   $253.25   $253.20  
  Purchase #7 $67.53   4.672%   $70.685   $70.69   $70.70   $70.70  
  7 purchase totals = $910.06       $996.5416   $996.56   $996.60   $996.50