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	$138.96	13.292%	$157.4306	$157.43	$157.45	$157.40
Purchase #2	$124.78	9.300%	$136.3845	$136.38	$136.40	$136.40
Purchase #3	$97.92	13.820%	$111.4525	$111.45	$111.45	$111.50
Purchase #4	$105.61	8.180%	$114.2489	$114.25	$114.25	$114.20
Purchase #5	$29.34	12.103%	$32.891	$32.89	$32.90	$32.90
Purchase #6	$73.27	5.252%	$77.1181	$77.12	$77.10	$77.10
Purchase #7	$248.46	11.669%	$277.4528	$277.45	$277.45	$277.50
7 purchase totals =	$818.34		$906.9784	$906.97	$907.00	$907.00