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	$48.89	4.149%	$50.9184	$50.92	$50.90	$50.90
Purchase #2	$75.49	12.874%	$85.2086	$85.21	$85.20	$85.20
Purchase #3	$185.74	7.271%	$199.2452	$199.25	$199.25	$199.20
Purchase #4	$139.76	9.733%	$153.3628	$153.36	$153.35	$153.40
Purchase #5	$213.78	13.123%	$241.8343	$241.83	$241.85	$241.80
Purchase #6	$37.84	12.661%	$42.6309	$42.63	$42.65	$42.60
Purchase #7	$237.90	9.362%	$260.1722	$260.17	$260.15	$260.20
7 purchase totals =	$939.40		$1,033.3724	$1,033.37	$1,033.35	$1,033.30