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	$32.67	3.388%	$33.7769	$33.78	$33.80	$33.80
Purchase #2	$30.51	8.807%	$33.197	$33.20	$33.20	$33.20
Purchase #3	$223.64	6.652%	$238.5165	$238.52	$238.50	$238.50
Purchase #4	$131.51	12.628%	$148.1171	$148.12	$148.10	$148.10
Purchase #5	$127.91	3.227%	$132.0377	$132.04	$132.05	$132.00
Purchase #6	$199.74	11.436%	$222.5823	$222.58	$222.60	$222.60
Purchase #7	$167.56	4.630%	$175.318	$175.32	$175.30	$175.30
7 purchase totals =	$913.54		$983.5455	$983.56	$983.55	$983.50