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	$90.31	6.343%	$96.0384	$96.04	$96.05	$96.00
Purchase #2	$100.95	10.334%	$111.3822	$111.38	$111.40	$111.40
Purchase #3	$10.62	5.773%	$11.2331	$11.23	$11.25	$11.20
Purchase #4	$120.92	8.854%	$131.6263	$131.63	$131.65	$131.60
Purchase #5	$84.40	4.561%	$88.2495	$88.25	$88.25	$88.20
Purchase #6	$74.40	10.353%	$82.1026	$82.10	$82.10	$82.10
Purchase #7	$33.29	3.563%	$34.4761	$34.48	$34.50	$34.50
7 purchase totals =	$514.89		$555.1082	$555.11	$555.20	$555.00