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	$238.77	12.531%	$268.6903	$268.69	$268.70	$268.70
Purchase #2	$56.72	5.480%	$59.8283	$59.83	$59.85	$59.80
Purchase #3	$75.27	4.855%	$78.9244	$78.92	$78.90	$78.90
Purchase #4	$116.66	8.201%	$126.2273	$126.23	$126.25	$126.20
Purchase #5	$158.99	3.848%	$165.1079	$165.11	$165.10	$165.10
Purchase #6	$221.73	13.484%	$251.6281	$251.63	$251.65	$251.60
Purchase #7	$67.82	9.137%	$74.0167	$74.02	$74.00	$74.00
7 purchase totals =	$935.96		$1,024.4230	$1,024.43	$1,024.45	$1,024.30