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	$123.37	3.431%	$127.6028	$127.60	$127.60	$127.60
Purchase #2	$214.41	3.105%	$221.0674	$221.07	$221.05	$221.10
Purchase #3	$250.82	9.630%	$274.974	$274.97	$274.95	$275.00
Purchase #4	$171.43	11.150%	$190.5444	$190.54	$190.55	$190.50
Purchase #5	$53.97	6.218%	$57.3259	$57.33	$57.35	$57.30
Purchase #6	$82.53	9.869%	$90.6749	$90.67	$90.65	$90.70
Purchase #7	$218.41	13.451%	$247.7883	$247.79	$247.80	$247.80
7 purchase totals =	$1,114.94		$1,209.9777	$1,209.97	$1,209.95	$1,210.00