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	$130.51	10.551%	$144.2801	$144.28	$144.30	$144.30
Purchase #2	$60.58	8.375%	$65.6536	$65.65	$65.65	$65.70
Purchase #3	$81.53	10.202%	$89.8477	$89.85	$89.85	$89.80
Purchase #4	$165.68	11.311%	$184.4201	$184.42	$184.40	$184.40
Purchase #5	$141.94	7.478%	$152.5543	$152.55	$152.55	$152.60
Purchase #6	$102.95	13.781%	$117.1375	$117.14	$117.15	$117.10
Purchase #7	$87.48	3.180%	$90.2619	$90.26	$90.25	$90.30
7 purchase totals =	$770.67		$844.1552	$844.15	$844.15	$844.20