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 $55.59   3.588%   $57.5846   $57.58   $57.60   $57.60  
  Purchase #2 $22.40   13.555%   $25.4363   $25.44   $25.45   $25.40  
  Purchase #3 $241.99   4.676%   $253.3055   $253.31   $253.30   $253.30  
  Purchase #4 $164.98   13.531%   $187.3034   $187.30   $187.30   $187.30  
  Purchase #5 $188.84   3.247%   $194.9716   $194.97   $194.95   $195.00  
  Purchase #6 $64.70   12.105%   $72.5319   $72.53   $72.55   $72.50  
  Purchase #7 $235.63   11.568%   $262.8877   $262.89   $262.90   $262.90  
  7 purchase totals = $974.13       $1,054.0210   $1,054.02   $1,054.05   $1,054.00