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 $230.80   10.465%   $254.9532   $254.95   $254.95   $255.00  
  Purchase #2 $64.47   11.720%   $72.0259   $72.03   $72.05   $72.00  
  Purchase #3 $13.68   7.759%   $14.7414   $14.74   $14.75   $14.70  
  Purchase #4 $246.27   4.522%   $257.4063   $257.41   $257.40   $257.40  
  Purchase #5 $170.40   6.150%   $180.8796   $180.88   $180.90   $180.90  
  Purchase #6 $23.86   6.524%   $25.4166   $25.42   $25.40   $25.40  
  Purchase #7 $238.43   9.675%   $261.4981   $261.50   $261.50   $261.50  
  7 purchase totals = $987.91       $1,066.9211   $1,066.93   $1,066.95   $1,066.90