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	$203.25	9.846%	$223.262	$223.26	$223.25	$223.30
Purchase #2	$117.45	9.402%	$128.4926	$128.49	$128.50	$128.50
Purchase #3	$57.37	8.436%	$62.2097	$62.21	$62.20	$62.20
Purchase #4	$155.43	11.569%	$173.4117	$173.41	$173.40	$173.40
Purchase #5	$48.51	3.388%	$50.1535	$50.15	$50.15	$50.20
Purchase #6	$167.39	10.784%	$185.4413	$185.44	$185.45	$185.40
Purchase #7	$118.78	11.580%	$132.5347	$132.53	$132.55	$132.50
7 purchase totals =	$868.18		$955.5055	$955.49	$955.50	$955.50