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	$92.89	8.168%	$100.4773	$100.48	$100.50	$100.50
Purchase #2	$39.93	7.104%	$42.7666	$42.77	$42.75	$42.80
Purchase #3	$153.31	4.324%	$159.9391	$159.94	$159.95	$159.90
Purchase #4	$149.58	4.180%	$155.8324	$155.83	$155.85	$155.80
Purchase #5	$81.29	5.427%	$85.7016	$85.70	$85.70	$85.70
Purchase #6	$225.61	11.766%	$252.1553	$252.16	$252.15	$252.20
Purchase #7	$195.32	5.228%	$205.5313	$205.53	$205.55	$205.50
7 purchase totals =	$937.93		$1,002.4036	$1,002.41	$1,002.45	$1,002.40