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 $90.52   5.517%   $95.514   $95.51   $95.50   $95.50  
  Purchase #2 $50.46   12.317%   $56.6752   $56.68   $56.70   $56.70  
  Purchase #3 $51.80   3.339%   $53.5296   $53.53   $53.55   $53.50  
  Purchase #4 $120.38   12.565%   $135.5057   $135.51   $135.50   $135.50  
  Purchase #5 $217.85   8.519%   $236.4086   $236.41   $236.40   $236.40  
  Purchase #6 $27.34   6.719%   $29.177   $29.18   $29.20   $29.20  
  Purchase #7 $200.89   12.472%   $225.945   $225.95   $225.95   $225.90  
  7 purchase totals = $759.24       $832.7551   $832.77   $832.80   $832.70