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 $78.53   5.161%   $82.5829   $82.58   $82.60   $82.60  
  Purchase #2 $157.69   5.573%   $166.4781   $166.48   $166.50   $166.50  
  Purchase #3 $85.87   13.162%   $97.1722   $97.17   $97.15   $97.20  
  Purchase #4 $188.42   13.324%   $213.5251   $213.53   $213.55   $213.50  
  Purchase #5 $5.75   5.262%   $6.0526   $6.05   $6.05   $6.10  
  Purchase #6 $44.82   10.753%   $49.6395   $49.64   $49.65   $49.60  
  Purchase #7 $99.91   10.624%   $110.5244   $110.52   $110.50   $110.50  
  7 purchase totals = $660.99       $725.9748   $725.97   $726.00   $726.00