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	$134.43	8.519%	$145.8821	$145.88	$145.90	$145.90
Purchase #2	$173.34	13.530%	$196.7929	$196.79	$196.80	$196.80
Purchase #3	$116.70	5.801%	$123.4698	$123.47	$123.45	$123.50
Purchase #4	$33.87	10.454%	$37.4108	$37.41	$37.40	$37.40
Purchase #5	$134.29	6.700%	$143.2874	$143.29	$143.30	$143.30
Purchase #6	$163.42	5.760%	$172.833	$172.83	$172.85	$172.80
Purchase #7	$20.87	3.505%	$21.6015	$21.60	$21.60	$21.60
7 purchase totals =	$776.92		$841.2775	$841.27	$841.30	$841.30