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	$133.29	9.151%	$145.4874	$145.49	$145.50	$145.50
Purchase #2	$20.48	5.727%	$21.6529	$21.65	$21.65	$21.70
Purchase #3	$59.64	7.583%	$64.1625	$64.16	$64.15	$64.20
Purchase #4	$155.74	11.414%	$173.5162	$173.52	$173.50	$173.50
Purchase #5	$86.61	13.368%	$98.188	$98.19	$98.20	$98.20
Purchase #6	$200.26	12.125%	$224.5415	$224.54	$224.55	$224.50
Purchase #7	$58.52	5.279%	$61.6093	$61.61	$61.60	$61.60
7 purchase totals =	$714.54		$789.1578	$789.16	$789.15	$789.20