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 $224.76   9.314%   $245.6941   $245.69   $245.70   $245.70  
  Purchase #2 $148.43   9.146%   $162.0054   $162.01   $162.00   $162.00  
  Purchase #3 $55.45   5.205%   $58.3362   $58.34   $58.35   $58.30  
  Purchase #4 $197.79   4.665%   $207.0169   $207.02   $207.00   $207.00  
  Purchase #5 $229.98   13.490%   $261.0043   $261.00   $261.00   $261.00  
  Purchase #6 $108.78   7.630%   $117.0799   $117.08   $117.10   $117.10  
  Purchase #7 $248.42   10.644%   $274.8618   $274.86   $274.85   $274.90  
  7 purchase totals = $1,213.61       $1,325.9986   $1,326.00   $1,326.00   $1,326.00