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	$247.65	7.331%	$265.8052	$265.81	$265.80	$265.80
Purchase #2	$117.83	8.733%	$128.1201	$128.12	$128.10	$128.10
Purchase #3	$40.76	11.485%	$45.4413	$45.44	$45.45	$45.40
Purchase #4	$234.72	3.641%	$243.2662	$243.27	$243.25	$243.30
Purchase #5	$59.73	4.336%	$62.3199	$62.32	$62.30	$62.30
Purchase #6	$57.94	8.665%	$62.9605	$62.96	$62.95	$63.00
Purchase #7	$60.73	3.446%	$62.8228	$62.82	$62.80	$62.80
7 purchase totals =	$819.36		$870.7360	$870.74	$870.65	$870.70