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 $200.31   7.780%   $215.8941   $215.89   $215.90   $215.90  
  Purchase #2 $250.38   8.344%   $271.2717   $271.27   $271.25   $271.30  
  Purchase #3 $85.48   10.806%   $94.717   $94.72   $94.70   $94.70  
  Purchase #4 $23.38   3.416%   $24.1787   $24.18   $24.20   $24.20  
  Purchase #5 $55.93   5.207%   $58.8423   $58.84   $58.85   $58.80  
  Purchase #6 $245.78   11.547%   $274.1602   $274.16   $274.15   $274.20  
  Purchase #7 $236.72   7.807%   $255.2007   $255.20   $255.20   $255.20  
  7 purchase totals = $1,097.98       $1,194.2647   $1,194.26   $1,194.25   $1,194.30