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 $23.49   8.724%   $25.5393   $25.54   $25.55   $25.50  
  Purchase #2 $215.59   13.522%   $244.7421   $244.74   $244.75   $244.70  
  Purchase #3 $121.27   9.613%   $132.9277   $132.93   $132.95   $132.90  
  Purchase #4 $206.96   10.400%   $228.4838   $228.48   $228.50   $228.50  
  Purchase #5 $240.88   13.817%   $274.1624   $274.16   $274.15   $274.20  
  Purchase #6 $114.68   11.707%   $128.1056   $128.11   $128.10   $128.10  
  Purchase #7 $239.42   7.666%   $257.7739   $257.77   $257.75   $257.80  
  7 purchase totals = $1,162.29       $1,291.7348   $1,291.73   $1,291.75   $1,291.70