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 $119.44   4.234%   $124.4971   $124.50   $124.50   $124.50  
  Purchase #2 $95.43   10.577%   $105.5236   $105.52   $105.50   $105.50  
  Purchase #3 $247.97   7.309%   $266.0941   $266.09   $266.10   $266.10  
  Purchase #4 $85.58   11.161%   $95.1316   $95.13   $95.15   $95.10  
  Purchase #5 $108.59   7.468%   $116.6995   $116.70   $116.70   $116.70  
  Purchase #6 $115.50   8.714%   $125.5647   $125.56   $125.55   $125.60  
  Purchase #7 $190.87   12.167%   $214.0932   $214.09   $214.10   $214.10  
  7 purchase totals = $963.38       $1,047.6038   $1,047.59   $1,047.60   $1,047.60