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 $217.88   12.408%   $244.9146   $244.91   $244.90   $244.90  
  Purchase #2 $112.86   11.314%   $125.629   $125.63   $125.65   $125.60  
  Purchase #3 $152.41   11.830%   $170.4401   $170.44   $170.45   $170.40  
  Purchase #4 $46.30   12.195%   $51.9463   $51.95   $51.95   $51.90  
  Purchase #5 $196.34   6.652%   $209.4005   $209.40   $209.40   $209.40  
  Purchase #6 $173.62   5.667%   $183.459   $183.46   $183.45   $183.50  
  Purchase #7 $108.91   6.859%   $116.3801   $116.38   $116.40   $116.40  
  7 purchase totals = $1,008.32       $1,102.1696   $1,102.17   $1,102.20   $1,102.10