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	$230.84	11.222%	$256.7449	$256.74	$256.75	$256.70
Purchase #2	$54.60	12.730%	$61.5506	$61.55	$61.55	$61.60
Purchase #3	$54.72	12.858%	$61.7559	$61.76	$61.75	$61.80
Purchase #4	$148.75	3.745%	$154.3207	$154.32	$154.30	$154.30
Purchase #5	$135.98	8.298%	$147.2636	$147.26	$147.25	$147.30
Purchase #6	$164.83	12.389%	$185.2508	$185.25	$185.25	$185.30
Purchase #7	$37.27	8.410%	$40.4044	$40.40	$40.40	$40.40
7 purchase totals =	$826.99		$907.2909	$907.28	$907.25	$907.40