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	$63.70	11.820%	$71.2293	$71.23	$71.25	$71.20
Purchase #2	$64.84	12.799%	$73.1389	$73.14	$73.15	$73.10
Purchase #3	$244.80	8.370%	$265.2898	$265.29	$265.30	$265.30
Purchase #4	$108.68	13.542%	$123.3974	$123.40	$123.40	$123.40
Purchase #5	$31.50	5.858%	$33.3453	$33.35	$33.35	$33.30
Purchase #6	$155.50	7.699%	$167.4719	$167.47	$167.45	$167.50
Purchase #7	$230.80	8.482%	$250.3765	$250.38	$250.40	$250.40
7 purchase totals =	$899.82		$984.2491	$984.26	$984.30	$984.20