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	$52.58	5.647%	$55.5492	$55.55	$55.55	$55.50
Purchase #2	$29.89	8.702%	$32.491	$32.49	$32.50	$32.50
Purchase #3	$93.85	8.144%	$101.4931	$101.49	$101.50	$101.50
Purchase #4	$172.27	7.456%	$185.1145	$185.11	$185.10	$185.10
Purchase #5	$244.86	7.830%	$264.0325	$264.03	$264.05	$264.00
Purchase #6	$77.76	10.803%	$86.1604	$86.16	$86.15	$86.20
Purchase #7	$73.72	12.613%	$83.0183	$83.02	$83.00	$83.00
7 purchase totals =	$744.93		$807.8590	$807.85	$807.85	$807.80