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 $29.70   4.142%   $30.9302   $30.93   $30.95   $30.90  
  Purchase #2 $200.72   6.685%   $214.1381   $214.14   $214.15   $214.10  
  Purchase #3 $26.89   9.533%   $29.4534   $29.45   $29.45   $29.50  
  Purchase #4 $69.44   13.295%   $78.672   $78.67   $78.65   $78.70  
  Purchase #5 $97.82   7.798%   $105.448   $105.45   $105.45   $105.40  
  Purchase #6 $14.77   11.215%   $16.4265   $16.43   $16.45   $16.40  
  Purchase #7 $148.64   8.609%   $161.4364   $161.44   $161.45   $161.40  
  7 purchase totals = $587.98       $636.5046   $636.51   $636.55   $636.40