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 $238.98   9.409%   $261.4656   $261.47   $261.45   $261.50  
  Purchase #2 $229.91   5.602%   $242.7896   $242.79   $242.80   $242.80  
  Purchase #3 $60.73   5.738%   $64.2147   $64.21   $64.20   $64.20  
  Purchase #4 $76.90   3.398%   $79.5131   $79.51   $79.50   $79.50  
  Purchase #5 $137.25   11.581%   $153.1449   $153.14   $153.15   $153.10  
  Purchase #6 $148.25   13.163%   $167.7641   $167.76   $167.75   $167.80  
  Purchase #7 $228.93   8.803%   $249.0827   $249.08   $249.10   $249.10  
  7 purchase totals = $1,120.95       $1,217.9747   $1,217.96   $1,217.95   $1,218.00