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	$106.30	11.414%	$118.4331	$118.43	$118.45	$118.40
Purchase #2	$90.59	4.364%	$94.5433	$94.54	$94.55	$94.50
Purchase #3	$88.74	13.394%	$100.6258	$100.63	$100.65	$100.60
Purchase #4	$67.90	9.699%	$74.4856	$74.49	$74.50	$74.50
Purchase #5	$51.38	11.222%	$57.1459	$57.15	$57.15	$57.10
Purchase #6	$247.62	9.529%	$271.2157	$271.22	$271.20	$271.20
Purchase #7	$110.60	6.619%	$117.9206	$117.92	$117.90	$117.90
7 purchase totals =	$763.13		$834.3700	$834.38	$834.40	$834.20