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	$9.31	10.194%	$10.2591	$10.26	$10.25	$10.30
Purchase #2	$34.92	6.361%	$37.1413	$37.14	$37.15	$37.10
Purchase #3	$96.57	9.745%	$105.9807	$105.98	$106.00	$106.00
Purchase #4	$62.39	5.490%	$65.8152	$65.82	$65.80	$65.80
Purchase #5	$122.73	6.760%	$131.0265	$131.03	$131.05	$131.00
Purchase #6	$134.79	8.565%	$146.3348	$146.33	$146.35	$146.30
Purchase #7	$49.74	11.561%	$55.4904	$55.49	$55.50	$55.50
7 purchase totals =	$510.45		$552.0480	$552.05	$552.10	$552.00