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	$225.77	11.510%	$251.7561	$251.76	$251.75	$251.80
Purchase #2	$104.83	6.233%	$111.3641	$111.36	$111.35	$111.40
Purchase #3	$38.25	3.231%	$39.4859	$39.49	$39.50	$39.50
Purchase #4	$131.72	4.313%	$137.4011	$137.40	$137.40	$137.40
Purchase #5	$247.55	12.228%	$277.8204	$277.82	$277.80	$277.80
Purchase #6	$51.85	8.563%	$56.2899	$56.29	$56.30	$56.30
Purchase #7	$113.51	13.765%	$129.1347	$129.13	$129.15	$129.10
7 purchase totals =	$913.48		$1,003.2522	$1,003.25	$1,003.25	$1,003.30