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 $182.98   6.526%   $194.9213   $194.92   $194.90   $194.90  
  Purchase #2 $124.32   7.645%   $133.8243   $133.82   $133.80   $133.80  
  Purchase #3 $22.65   9.710%   $24.8493   $24.85   $24.85   $24.80  
  Purchase #4 $208.34   13.466%   $236.3951   $236.40   $236.40   $236.40  
  Purchase #5 $74.94   12.526%   $84.327   $84.33   $84.35   $84.30  
  Purchase #6 $234.25   11.735%   $261.7392   $261.74   $261.75   $261.70  
  Purchase #7 $81.59   5.296%   $85.911   $85.91   $85.90   $85.90  
  7 purchase totals = $929.07       $1,021.9672   $1,021.97   $1,021.95   $1,021.80