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	$31.28	3.858%	$32.4868	$32.49	$32.50	$32.50
Purchase #2	$21.68	6.625%	$23.1163	$23.12	$23.10	$23.10
Purchase #3	$22.54	13.718%	$25.632	$25.63	$25.65	$25.60
Purchase #4	$115.90	10.361%	$127.9084	$127.91	$127.90	$127.90
Purchase #5	$97.33	8.700%	$105.7977	$105.80	$105.80	$105.80
Purchase #6	$207.44	7.751%	$223.5187	$223.52	$223.50	$223.50
Purchase #7	$244.53	4.118%	$254.5997	$254.60	$254.60	$254.60
7 purchase totals =	$740.70		$793.0596	$793.07	$793.05	$793.00