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	$222.76	4.791%	$233.4324	$233.43	$233.45	$233.40
Purchase #2	$198.34	13.614%	$225.342	$225.34	$225.35	$225.30
Purchase #3	$52.72	11.205%	$58.6273	$58.63	$58.65	$58.60
Purchase #4	$73.39	12.777%	$82.767	$82.77	$82.75	$82.80
Purchase #5	$71.85	7.847%	$77.4881	$77.49	$77.50	$77.50
Purchase #6	$125.66	5.809%	$132.9596	$132.96	$132.95	$133.00
Purchase #7	$115.41	10.734%	$127.7981	$127.80	$127.80	$127.80
7 purchase totals =	$860.13		$938.4145	$938.42	$938.45	$938.40