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 $65.95   11.799%   $73.7314   $73.73   $73.75   $73.70  
  Purchase #2 $50.48   9.424%   $55.2372   $55.24   $55.25   $55.20  
  Purchase #3 $210.63   3.859%   $218.7582   $218.76   $218.75   $218.80  
  Purchase #4 $31.45   3.673%   $32.6052   $32.61   $32.60   $32.60  
  Purchase #5 $9.71   10.674%   $10.7464   $10.75   $10.75   $10.70  
  Purchase #6 $179.97   4.795%   $188.5996   $188.60   $188.60   $188.60  
  Purchase #7 $249.86   6.705%   $266.6131   $266.61   $266.60   $266.60  
  7 purchase totals = $798.05       $846.2911   $846.30   $846.30   $846.20