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 $205.56   11.473%   $229.1439   $229.14   $229.15   $229.10  
  Purchase #2 $180.42   10.431%   $199.2396   $199.24   $199.25   $199.20  
  Purchase #3 $57.53   5.555%   $60.7258   $60.73   $60.75   $60.70  
  Purchase #4 $98.47   3.841%   $102.2522   $102.25   $102.25   $102.30  
  Purchase #5 $212.99   7.577%   $229.1283   $229.13   $229.15   $229.10  
  Purchase #6 $250.86   12.871%   $283.1482   $283.15   $283.15   $283.10  
  Purchase #7 $156.26   9.177%   $170.6   $170.60   $170.60   $170.60  
  7 purchase totals = $1,162.09       $1,274.2380   $1,274.24   $1,274.30   $1,274.10