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 $209.59   3.221%   $216.3409   $216.34   $216.35   $216.30  
  Purchase #2 $88.46   4.793%   $92.6999   $92.70   $92.70   $92.70  
  Purchase #3 $195.76   6.207%   $207.9108   $207.91   $207.90   $207.90  
  Purchase #4 $250.84   4.175%   $261.3126   $261.31   $261.30   $261.30  
  Purchase #5 $123.42   11.162%   $137.1961   $137.20   $137.20   $137.20  
  Purchase #6 $50.57   13.464%   $57.3787   $57.38   $57.40   $57.40  
  Purchase #7 $56.55   9.813%   $62.0993   $62.10   $62.10   $62.10  
  7 purchase totals = $975.19       $1,034.9383   $1,034.94   $1,034.95   $1,034.90