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 $216.73   9.678%   $237.7051   $237.71   $237.70   $237.70  
  Purchase #2 $146.44   8.244%   $158.5125   $158.51   $158.50   $158.50  
  Purchase #3 $116.51   11.667%   $130.1032   $130.10   $130.10   $130.10  
  Purchase #4 $57.83   7.703%   $62.2846   $62.28   $62.30   $62.30  
  Purchase #5 $101.53   4.607%   $106.2075   $106.21   $106.20   $106.20  
  Purchase #6 $62.62   8.123%   $67.7066   $67.71   $67.70   $67.70  
  Purchase #7 $113.82   4.689%   $119.157   $119.16   $119.15   $119.20  
  7 purchase totals = $815.48       $881.6765   $881.68   $881.65   $881.70