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	$115.72	9.240%	$126.4125	$126.41	$126.40	$126.40
Purchase #2	$164.67	9.296%	$179.9777	$179.98	$180.00	$180.00
Purchase #3	$152.28	4.521%	$159.1646	$159.16	$159.15	$159.20
Purchase #4	$131.82	10.781%	$146.0315	$146.03	$146.05	$146.00
Purchase #5	$88.81	12.194%	$99.6395	$99.64	$99.65	$99.60
Purchase #6	$12.72	9.528%	$13.932	$13.93	$13.95	$13.90
Purchase #7	$152.72	7.599%	$164.3252	$164.33	$164.35	$164.30
7 purchase totals =	$818.74		$889.4830	$889.48	$889.55	$889.40