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 $217.71   11.498%   $242.7423   $242.74   $242.75   $242.70  
  Purchase #2 $204.69   13.307%   $231.9281   $231.93   $231.95   $231.90  
  Purchase #3 $51.46   10.676%   $56.9539   $56.95   $56.95   $57.00  
  Purchase #4 $34.27   8.258%   $37.1   $37.10   $37.10   $37.10  
  Purchase #5 $238.69   12.374%   $268.2255   $268.23   $268.25   $268.20  
  Purchase #6 $248.32   6.560%   $264.6098   $264.61   $264.60   $264.60  
  Purchase #7 $100.52   12.754%   $113.3403   $113.34   $113.35   $113.30  
  7 purchase totals = $1,095.66       $1,214.8999   $1,214.90   $1,214.95   $1,214.80