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 $41.97   8.313%   $45.459   $45.46   $45.45   $45.50  
  Purchase #2 $112.90   11.489%   $125.8711   $125.87   $125.85   $125.90  
  Purchase #3 $95.33   9.664%   $104.5427   $104.54   $104.55   $104.50  
  Purchase #4 $179.82   11.837%   $201.1053   $201.11   $201.10   $201.10  
  Purchase #5 $199.71   8.601%   $216.8871   $216.89   $216.90   $216.90  
  Purchase #6 $184.79   12.348%   $207.6079   $207.61   $207.60   $207.60  
  Purchase #7 $216.43   11.353%   $241.0013   $241.00   $241.00   $241.00  
  7 purchase totals = $1,030.95       $1,142.4744   $1,142.48   $1,142.45   $1,142.50