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	$92.67	8.362%	$100.4191	$100.42	$100.40	$100.40
Purchase #2	$99.73	11.340%	$111.0394	$111.04	$111.05	$111.00
Purchase #3	$7.62	6.375%	$8.1058	$8.11	$8.10	$8.10
Purchase #4	$116.55	12.142%	$130.7015	$130.70	$130.70	$130.70
Purchase #5	$207.92	4.479%	$217.2327	$217.23	$217.25	$217.20
Purchase #6	$165.72	3.665%	$171.7936	$171.79	$171.80	$171.80
Purchase #7	$78.55	9.370%	$85.9101	$85.91	$85.90	$85.90
7 purchase totals =	$768.76		$825.2022	$825.20	$825.20	$825.10