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 $211.66   8.811%   $230.3094   $230.31   $230.30   $230.30  
  Purchase #2 $141.95   7.821%   $153.0519   $153.05   $153.05   $153.10  
  Purchase #3 $236.67   9.329%   $258.7489   $258.75   $258.75   $258.70  
  Purchase #4 $46.81   5.375%   $49.326   $49.33   $49.35   $49.30  
  Purchase #5 $19.77   12.584%   $22.2579   $22.26   $22.25   $22.30  
  Purchase #6 $239.42   9.309%   $261.7076   $261.71   $261.70   $261.70  
  Purchase #7 $87.98   4.532%   $91.9673   $91.97   $91.95   $92.00  
  7 purchase totals = $984.26       $1,067.3690   $1,067.38   $1,067.35   $1,067.40