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 $190.73   10.117%   $210.0262   $210.03   $210.05   $210.00  
  Purchase #2 $164.88   8.322%   $178.6013   $178.60   $178.60   $178.60  
  Purchase #3 $170.40   4.287%   $177.705   $177.71   $177.70   $177.70  
  Purchase #4 $86.91   8.581%   $94.3677   $94.37   $94.35   $94.40  
  Purchase #5 $177.60   13.106%   $200.8763   $200.88   $200.90   $200.90  
  Purchase #6 $125.40   11.448%   $139.7558   $139.76   $139.75   $139.80  
  Purchase #7 $237.48   3.126%   $244.9036   $244.90   $244.90   $244.90  
  7 purchase totals = $1,153.40       $1,246.2359   $1,246.25   $1,246.25   $1,246.30