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	$250.32	10.748%	$277.2244	$277.22	$277.20	$277.20
Purchase #2	$40.43	12.483%	$45.4769	$45.48	$45.50	$45.50
Purchase #3	$125.78	10.750%	$139.3014	$139.30	$139.30	$139.30
Purchase #4	$129.82	7.154%	$139.1073	$139.11	$139.10	$139.10
Purchase #5	$195.64	13.448%	$221.9497	$221.95	$221.95	$221.90
Purchase #6	$130.32	13.116%	$147.4128	$147.41	$147.40	$147.40
Purchase #7	$93.42	7.433%	$100.3639	$100.36	$100.35	$100.40
7 purchase totals =	$965.73		$1,070.8364	$1,070.83	$1,070.80	$1,070.80