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	$10.76	12.853%	$12.143	$12.14	$12.15	$12.10
Purchase #2	$152.73	10.171%	$168.2642	$168.26	$168.25	$168.30
Purchase #3	$68.59	8.533%	$74.4428	$74.44	$74.45	$74.40
Purchase #4	$205.39	13.583%	$233.2881	$233.29	$233.30	$233.30
Purchase #5	$89.34	12.449%	$100.4619	$100.46	$100.45	$100.50
Purchase #6	$26.48	8.520%	$28.7361	$28.74	$28.75	$28.70
Purchase #7	$108.95	8.834%	$118.5746	$118.57	$118.55	$118.60
7 purchase totals =	$662.24		$735.9107	$735.90	$735.90	$735.90