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 $24.41   9.569%   $26.7458   $26.75   $26.75   $26.70  
  Purchase #2 $198.30   13.503%   $225.0764   $225.08   $225.10   $225.10  
  Purchase #3 $101.37   13.869%   $115.429   $115.43   $115.45   $115.40  
  Purchase #4 $94.42   3.402%   $97.6322   $97.63   $97.65   $97.60  
  Purchase #5 $96.45   6.580%   $102.7964   $102.80   $102.80   $102.80  
  Purchase #6 $78.84   4.182%   $82.1371   $82.14   $82.15   $82.10  
  Purchase #7 $15.94   4.265%   $16.6198   $16.62   $16.60   $16.60  
  7 purchase totals = $609.73       $666.4367   $666.45   $666.50   $666.30