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	$35.53	13.156%	$40.2043	$40.20	$40.20	$40.20
Purchase #2	$227.35	12.327%	$255.3754	$255.38	$255.40	$255.40
Purchase #3	$71.89	11.765%	$80.3479	$80.35	$80.35	$80.30
Purchase #4	$156.87	10.786%	$173.79	$173.79	$173.80	$173.80
Purchase #5	$136.29	10.576%	$150.704	$150.70	$150.70	$150.70
Purchase #6	$93.92	8.521%	$101.9229	$101.92	$101.90	$101.90
Purchase #7	$184.86	8.566%	$200.6951	$200.70	$200.70	$200.70
7 purchase totals =	$906.71		$1,003.0396	$1,003.04	$1,003.05	$1,003.00