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 $235.98   10.614%   $261.0269   $261.03   $261.05   $261.00  
  Purchase #2 $116.62   13.579%   $132.4558   $132.46   $132.45   $132.50  
  Purchase #3 $50.91   3.574%   $52.7295   $52.73   $52.75   $52.70  
  Purchase #4 $56.42   3.839%   $58.586   $58.59   $58.60   $58.60  
  Purchase #5 $98.93   11.364%   $110.1724   $110.17   $110.15   $110.20  
  Purchase #6 $177.97   8.222%   $192.6027   $192.60   $192.60   $192.60  
  Purchase #7 $96.68   9.436%   $105.8027   $105.80   $105.80   $105.80  
  7 purchase totals = $833.51       $913.3760   $913.38   $913.40   $913.40