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 $184.28   12.680%   $207.6467   $207.65   $207.65   $207.60  
  Purchase #2 $76.36   7.836%   $82.3436   $82.34   $82.35   $82.30  
  Purchase #3 $23.72   11.674%   $26.4891   $26.49   $26.50   $26.50  
  Purchase #4 $194.77   9.213%   $212.7142   $212.71   $212.70   $212.70  
  Purchase #5 $193.73   10.702%   $214.463   $214.46   $214.45   $214.50  
  Purchase #6 $23.83   3.854%   $24.7484   $24.75   $24.75   $24.70  
  Purchase #7 $30.70   11.403%   $34.2007   $34.20   $34.20   $34.20  
  7 purchase totals = $727.39       $802.6057   $802.60   $802.60   $802.50