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	$159.45	3.285%	$164.6879	$164.69	$164.70	$164.70
Purchase #2	$37.82	3.460%	$39.1286	$39.13	$39.15	$39.10
Purchase #3	$40.68	11.490%	$45.3541	$45.35	$45.35	$45.40
Purchase #4	$10.43	7.851%	$11.2489	$11.25	$11.25	$11.20
Purchase #5	$106.53	8.670%	$115.7662	$115.77	$115.75	$115.80
Purchase #6	$94.68	5.472%	$99.8609	$99.86	$99.85	$99.90
Purchase #7	$172.85	10.133%	$190.3649	$190.36	$190.35	$190.40
7 purchase totals =	$622.44		$666.4115	$666.41	$666.40	$666.50