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 $48.70   13.475%   $55.2623   $55.26   $55.25   $55.30  
  Purchase #2 $224.42   5.205%   $236.1011   $236.10   $236.10   $236.10  
  Purchase #3 $63.64   11.693%   $71.0814   $71.08   $71.10   $71.10  
  Purchase #4 $46.40   5.468%   $48.9372   $48.94   $48.95   $48.90  
  Purchase #5 $62.31   13.543%   $70.7486   $70.75   $70.75   $70.70  
  Purchase #6 $246.96   10.558%   $273.034   $273.03   $273.05   $273.00  
  Purchase #7 $117.37   8.361%   $127.1833   $127.18   $127.20   $127.20  
  7 purchase totals = $809.80       $882.3479   $882.34   $882.40   $882.30