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 $54.41   5.464%   $57.383   $57.38   $57.40   $57.40  
  Purchase #2 $73.37   7.438%   $78.8273   $78.83   $78.85   $78.80  
  Purchase #3 $95.92   13.586%   $108.9517   $108.95   $108.95   $109.00  
  Purchase #4 $169.56   8.281%   $183.6013   $183.60   $183.60   $183.60  
  Purchase #5 $46.39   11.458%   $51.7054   $51.71   $51.70   $51.70  
  Purchase #6 $130.31   11.514%   $145.3139   $145.31   $145.30   $145.30  
  Purchase #7 $108.80   11.869%   $121.7135   $121.71   $121.70   $121.70  
  7 purchase totals = $678.76       $747.4961   $747.49   $747.50   $747.50