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	$232.91	9.167%	$254.2609	$254.26	$254.25	$254.30
Purchase #2	$106.43	4.471%	$111.1885	$111.19	$111.20	$111.20
Purchase #3	$242.50	10.706%	$268.4621	$268.46	$268.45	$268.50
Purchase #4	$145.56	6.733%	$155.3606	$155.36	$155.35	$155.40
Purchase #5	$43.76	3.403%	$45.2492	$45.25	$45.25	$45.20
Purchase #6	$54.46	3.665%	$56.456	$56.46	$56.45	$56.50
Purchase #7	$75.84	3.112%	$78.2001	$78.20	$78.20	$78.20
7 purchase totals =	$901.46		$969.1774	$969.18	$969.15	$969.30