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 $232.76   8.466%   $252.4655   $252.47   $252.45   $252.50  
  Purchase #2 $89.62   4.374%   $93.54   $93.54   $93.55   $93.50  
  Purchase #3 $104.98   12.636%   $118.2453   $118.25   $118.25   $118.20  
  Purchase #4 $107.75   6.290%   $114.5275   $114.53   $114.55   $114.50  
  Purchase #5 $246.46   4.737%   $258.1348   $258.13   $258.15   $258.10  
  Purchase #6 $84.98   10.327%   $93.7559   $93.76   $93.75   $93.80  
  Purchase #7 $19.71   6.222%   $20.9364   $20.94   $20.95   $20.90  
  7 purchase totals = $886.26       $951.6054   $951.62   $951.65   $951.50