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	$85.59	5.827%	$90.5773	$90.58	$90.60	$90.60
Purchase #2	$182.62	4.215%	$190.3174	$190.32	$190.30	$190.30
Purchase #3	$128.74	11.801%	$143.9326	$143.93	$143.95	$143.90
Purchase #4	$247.60	12.140%	$277.6586	$277.66	$277.65	$277.70
Purchase #5	$133.99	7.796%	$144.4359	$144.44	$144.45	$144.40
Purchase #6	$230.83	3.717%	$239.41	$239.41	$239.40	$239.40
Purchase #7	$35.79	3.313%	$36.9757	$36.98	$37.00	$37.00
7 purchase totals =	$1,045.16		$1,123.3075	$1,123.32	$1,123.35	$1,123.30