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 $56.68   6.568%   $60.4027   $60.40   $60.40   $60.40  
  Purchase #2 $141.78   13.294%   $160.6282   $160.63   $160.65   $160.60  
  Purchase #3 $236.54   5.528%   $249.6159   $249.62   $249.60   $249.60  
  Purchase #4 $237.33   9.793%   $260.5717   $260.57   $260.55   $260.60  
  Purchase #5 $250.37   8.243%   $271.008   $271.01   $271.00   $271.00  
  Purchase #6 $162.73   11.159%   $180.889   $180.89   $180.90   $180.90  
  Purchase #7 $158.71   12.129%   $177.9599   $177.96   $177.95   $178.00  
  7 purchase totals = $1,244.14       $1,361.0754   $1,361.08   $1,361.05   $1,361.10