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 $250.34   9.694%   $274.608   $274.61   $274.60   $274.60  
  Purchase #2 $18.62   6.799%   $19.886   $19.89   $19.90   $19.90  
  Purchase #3 $98.61   3.497%   $102.0584   $102.06   $102.05   $102.10  
  Purchase #4 $65.57   3.554%   $67.9004   $67.90   $67.90   $67.90  
  Purchase #5 $108.99   5.810%   $115.3223   $115.32   $115.30   $115.30  
  Purchase #6 $158.27   3.429%   $163.6971   $163.70   $163.70   $163.70  
  Purchase #7 $152.60   3.474%   $157.9013   $157.90   $157.90   $157.90  
  7 purchase totals = $853.00       $901.3735   $901.38   $901.35   $901.40