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 $211.71   7.785%   $228.1916   $228.19   $228.20   $228.20  
  Purchase #2 $34.74   8.722%   $37.77   $37.77   $37.75   $37.80  
  Purchase #3 $57.57   8.371%   $62.3892   $62.39   $62.40   $62.40  
  Purchase #4 $241.61   13.665%   $274.626   $274.63   $274.65   $274.60  
  Purchase #5 $206.34   8.747%   $224.3886   $224.39   $224.40   $224.40  
  Purchase #6 $41.77   6.297%   $44.4003   $44.40   $44.40   $44.40  
  Purchase #7 $90.46   6.551%   $96.386   $96.39   $96.40   $96.40  
  7 purchase totals = $884.20       $968.1517   $968.16   $968.20   $968.20