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	$181.81	3.655%	$188.4552	$188.46	$188.45	$188.50
Purchase #2	$229.57	5.819%	$242.9287	$242.93	$242.95	$242.90
Purchase #3	$77.34	4.518%	$80.8342	$80.83	$80.85	$80.80
Purchase #4	$212.77	8.160%	$230.132	$230.13	$230.15	$230.10
Purchase #5	$221.70	7.671%	$238.7066	$238.71	$238.70	$238.70
Purchase #6	$121.42	5.123%	$127.6403	$127.64	$127.65	$127.60
Purchase #7	$162.82	5.314%	$171.4723	$171.47	$171.45	$171.50
7 purchase totals =	$1,207.43		$1,280.1693	$1,280.17	$1,280.20	$1,280.10