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	$54.74	5.213%	$57.5936	$57.59	$57.60	$57.60
Purchase #2	$141.34	4.239%	$147.3314	$147.33	$147.35	$147.30
Purchase #3	$149.90	4.394%	$156.4866	$156.49	$156.50	$156.50
Purchase #4	$166.73	7.823%	$179.7733	$179.77	$179.75	$179.80
Purchase #5	$67.42	7.188%	$72.2661	$72.27	$72.25	$72.30
Purchase #6	$238.90	5.797%	$252.749	$252.75	$252.75	$252.70
Purchase #7	$152.46	13.797%	$173.4949	$173.49	$173.50	$173.50
7 purchase totals =	$971.49		$1,039.6949	$1,039.69	$1,039.70	$1,039.70