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	$73.26	6.841%	$78.2717	$78.27	$78.25	$78.30
Purchase #2	$34.64	9.194%	$37.8248	$37.82	$37.80	$37.80
Purchase #3	$9.73	7.376%	$10.4477	$10.45	$10.45	$10.40
Purchase #4	$209.37	7.596%	$225.2737	$225.27	$225.25	$225.30
Purchase #5	$153.33	9.329%	$167.6342	$167.63	$167.65	$167.60
Purchase #6	$220.50	12.194%	$247.3878	$247.39	$247.40	$247.40
Purchase #7	$121.30	4.551%	$126.8204	$126.82	$126.80	$126.80
7 purchase totals =	$822.13		$893.6603	$893.65	$893.60	$893.60