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 $54.88   6.528%   $58.4626   $58.46   $58.45   $58.50  
  Purchase #2 $234.49   6.592%   $249.9476   $249.95   $249.95   $249.90  
  Purchase #3 $114.94   9.795%   $126.1984   $126.20   $126.20   $126.20  
  Purchase #4 $84.69   8.429%   $91.8285   $91.83   $91.85   $91.80  
  Purchase #5 $135.79   7.787%   $146.364   $146.36   $146.35   $146.40  
  Purchase #6 $83.52   13.591%   $94.8712   $94.87   $94.85   $94.90  
  Purchase #7 $237.36   9.317%   $259.4748   $259.47   $259.45   $259.50  
  7 purchase totals = $945.67       $1,027.1471   $1,027.14   $1,027.10   $1,027.20