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	$160.77	11.733%	$179.6331	$179.63	$179.65	$179.60
Purchase #2	$88.29	4.748%	$92.482	$92.48	$92.50	$92.50
Purchase #3	$144.28	7.714%	$155.4098	$155.41	$155.40	$155.40
Purchase #4	$116.37	9.751%	$127.7172	$127.72	$127.70	$127.70
Purchase #5	$41.93	8.382%	$45.4446	$45.44	$45.45	$45.40
Purchase #6	$61.77	9.428%	$67.5937	$67.59	$67.60	$67.60
Purchase #7	$137.32	3.471%	$142.0864	$142.09	$142.10	$142.10
7 purchase totals =	$750.73		$810.3668	$810.36	$810.40	$810.30