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 $69.32   8.214%   $75.0139   $75.01   $75.00   $75.00  
  Purchase #2 $229.60   10.863%   $254.5414   $254.54   $254.55   $254.50  
  Purchase #3 $149.26   3.316%   $154.2095   $154.21   $154.20   $154.20  
  Purchase #4 $117.36   11.218%   $130.5254   $130.53   $130.55   $130.50  
  Purchase #5 $153.72   4.863%   $161.1954   $161.20   $161.20   $161.20  
  Purchase #6 $163.99   11.399%   $182.6832   $182.68   $182.70   $182.70  
  Purchase #7 $228.73   9.387%   $250.2009   $250.20   $250.20   $250.20  
  7 purchase totals = $1,111.98       $1,208.3697   $1,208.37   $1,208.40   $1,208.30