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 $179.98   11.762%   $201.1492   $201.15   $201.15   $201.10  
  Purchase #2 $97.39   7.417%   $104.6134   $104.61   $104.60   $104.60  
  Purchase #3 $60.42   12.703%   $68.0952   $68.10   $68.10   $68.10  
  Purchase #4 $53.40   13.824%   $60.782   $60.78   $60.80   $60.80  
  Purchase #5 $81.61   13.104%   $92.3042   $92.30   $92.30   $92.30  
  Purchase #6 $178.98   8.616%   $194.4009   $194.40   $194.40   $194.40  
  Purchase #7 $124.29   10.874%   $137.8053   $137.81   $137.80   $137.80  
  7 purchase totals = $776.07       $859.1502   $859.15   $859.15   $859.10