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 $228.75   11.802%   $255.7471   $255.75   $255.75   $255.70  
  Purchase #2 $205.71   5.470%   $216.9623   $216.96   $216.95   $217.00  
  Purchase #3 $53.73   8.489%   $58.2911   $58.29   $58.30   $58.30  
  Purchase #4 $195.95   13.127%   $221.6724   $221.67   $221.65   $221.70  
  Purchase #5 $82.38   11.641%   $91.9699   $91.97   $91.95   $92.00  
  Purchase #6 $202.81   11.428%   $225.9871   $225.99   $226.00   $226.00  
  Purchase #7 $81.66   13.829%   $92.9528   $92.95   $92.95   $93.00  
  7 purchase totals = $1,050.99       $1,163.5827   $1,163.58   $1,163.55   $1,163.70