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	$146.48	13.703%	$166.5522	$166.55	$166.55	$166.60
Purchase #2	$50.94	5.682%	$53.8344	$53.83	$53.85	$53.80
Purchase #3	$152.87	13.431%	$173.402	$173.40	$173.40	$173.40
Purchase #4	$182.53	3.647%	$189.1869	$189.19	$189.20	$189.20
Purchase #5	$40.60	4.546%	$42.4457	$42.45	$42.45	$42.40
Purchase #6	$33.62	11.623%	$37.5277	$37.53	$37.55	$37.50
Purchase #7	$10.51	11.608%	$11.73	$11.73	$11.75	$11.70
7 purchase totals =	$617.55		$674.6789	$674.68	$674.75	$674.60