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 $187.50   11.846%   $209.7113   $209.71   $209.70   $209.70  
  Purchase #2 $115.76   8.817%   $125.9666   $125.97   $125.95   $126.00  
  Purchase #3 $57.63   5.164%   $60.606   $60.61   $60.60   $60.60  
  Purchase #4 $245.76   5.223%   $258.596   $258.60   $258.60   $258.60  
  Purchase #5 $223.40   5.238%   $235.1017   $235.10   $235.10   $235.10  
  Purchase #6 $8.68   13.581%   $9.8588   $9.86   $9.85   $9.90  
  Purchase #7 $64.61   4.519%   $67.5297   $67.53   $67.55   $67.50  
  7 purchase totals = $903.34       $967.3701   $967.38   $967.35   $967.40