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 $47.81   10.530%   $52.8444   $52.84   $52.85   $52.80  
  Purchase #2 $126.87   11.359%   $141.2812   $141.28   $141.30   $141.30  
  Purchase #3 $211.71   5.660%   $223.6928   $223.69   $223.70   $223.70  
  Purchase #4 $14.29   10.284%   $15.7596   $15.76   $15.75   $15.80  
  Purchase #5 $213.32   13.657%   $242.4531   $242.45   $242.45   $242.50  
  Purchase #6 $70.41   7.830%   $75.9231   $75.92   $75.90   $75.90  
  Purchase #7 $76.83   10.305%   $84.7473   $84.75   $84.75   $84.70  
  7 purchase totals = $761.24       $836.7015   $836.69   $836.70   $836.70