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	$11.42	11.791%	$12.7665	$12.77	$12.75	$12.80
Purchase #2	$224.53	11.690%	$250.7776	$250.78	$250.80	$250.80
Purchase #3	$193.61	11.844%	$216.5412	$216.54	$216.55	$216.50
Purchase #4	$167.30	3.675%	$173.4483	$173.45	$173.45	$173.40
Purchase #5	$137.63	4.836%	$144.2858	$144.29	$144.30	$144.30
Purchase #6	$146.58	13.783%	$166.7831	$166.78	$166.80	$166.80
Purchase #7	$147.81	8.441%	$160.2866	$160.29	$160.30	$160.30
7 purchase totals =	$1,028.88		$1,124.8891	$1,124.90	$1,124.95	$1,124.90