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 $54.63   10.226%   $60.2165   $60.22   $60.20   $60.20  
  Purchase #2 $151.73   5.256%   $159.7049   $159.70   $159.70   $159.70  
  Purchase #3 $65.78   12.146%   $73.7696   $73.77   $73.75   $73.80  
  Purchase #4 $108.66   11.483%   $121.1374   $121.14   $121.15   $121.10  
  Purchase #5 $107.27   4.789%   $112.4072   $112.41   $112.40   $112.40  
  Purchase #6 $67.59   6.419%   $71.9286   $71.93   $71.95   $71.90  
  Purchase #7 $168.30   7.187%   $180.3957   $180.40   $180.40   $180.40  
  7 purchase totals = $723.96       $779.5599   $779.57   $779.55   $779.50