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 $101.34   12.756%   $114.2669   $114.27   $114.25   $114.30  
  Purchase #2 $95.62   7.440%   $102.7341   $102.73   $102.75   $102.70  
  Purchase #3 $236.88   8.485%   $256.9793   $256.98   $257.00   $257.00  
  Purchase #4 $211.42   6.854%   $225.9107   $225.91   $225.90   $225.90  
  Purchase #5 $180.57   10.654%   $199.8079   $199.81   $199.80   $199.80  
  Purchase #6 $119.88   6.239%   $127.3593   $127.36   $127.35   $127.40  
  Purchase #7 $180.92   10.775%   $200.4141   $200.41   $200.40   $200.40  
  7 purchase totals = $1,126.63       $1,227.4723   $1,227.47   $1,227.45   $1,227.50