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 $115.84   3.146%   $119.4843   $119.48   $119.50   $119.50  
  Purchase #2 $34.40   7.289%   $36.9074   $36.91   $36.90   $36.90  
  Purchase #3 $161.69   7.721%   $174.1741   $174.17   $174.15   $174.20  
  Purchase #4 $81.43   12.221%   $91.3816   $91.38   $91.40   $91.40  
  Purchase #5 $168.53   13.239%   $190.8417   $190.84   $190.85   $190.80  
  Purchase #6 $225.71   4.819%   $236.587   $236.59   $236.60   $236.60  
  Purchase #7 $234.46   11.323%   $261.0079   $261.01   $261.00   $261.00  
  7 purchase totals = $1,022.06       $1,110.3840   $1,110.38   $1,110.40   $1,110.40