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	$147.30	11.658%	$164.4722	$164.47	$164.45	$164.50
Purchase #2	$51.49	7.127%	$55.1597	$55.16	$55.15	$55.20
Purchase #3	$114.80	4.733%	$120.2335	$120.23	$120.25	$120.20
Purchase #4	$64.82	10.156%	$71.4031	$71.40	$71.40	$71.40
Purchase #5	$82.70	9.689%	$90.7128	$90.71	$90.70	$90.70
Purchase #6	$138.77	7.603%	$149.3207	$149.32	$149.30	$149.30
Purchase #7	$33.53	11.497%	$37.3849	$37.38	$37.40	$37.40
7 purchase totals =	$633.41		$688.6869	$688.67	$688.65	$688.70