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	$142.79	4.629%	$149.3997	$149.40	$149.40	$149.40
Purchase #2	$158.28	13.802%	$180.1258	$180.13	$180.15	$180.10
Purchase #3	$10.46	7.321%	$11.2258	$11.23	$11.25	$11.20
Purchase #4	$190.46	12.696%	$214.6408	$214.64	$214.65	$214.60
Purchase #5	$89.42	11.215%	$99.4485	$99.45	$99.45	$99.40
Purchase #6	$93.51	4.401%	$97.6254	$97.63	$97.65	$97.60
Purchase #7	$115.42	10.476%	$127.5114	$127.51	$127.50	$127.50
7 purchase totals =	$800.34		$879.9774	$879.99	$880.05	$879.80