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 $76.73   11.224%   $85.3422   $85.34   $85.35   $85.30  
  Purchase #2 $176.81   8.136%   $191.1953   $191.20   $191.20   $191.20  
  Purchase #3 $42.69   12.518%   $48.0339   $48.03   $48.05   $48.00  
  Purchase #4 $154.25   7.464%   $165.7632   $165.76   $165.75   $165.80  
  Purchase #5 $56.81   10.212%   $62.6114   $62.61   $62.60   $62.60  
  Purchase #6 $116.58   13.404%   $132.2064   $132.21   $132.20   $132.20  
  Purchase #7 $230.55   13.459%   $261.5797   $261.58   $261.60   $261.60  
  7 purchase totals = $854.42       $946.7321   $946.73   $946.75   $946.70