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	$69.71	12.491%	$78.4175	$78.42	$78.40	$78.40
Purchase #2	$231.92	9.362%	$253.6324	$253.63	$253.65	$253.60
Purchase #3	$144.70	9.816%	$158.9038	$158.90	$158.90	$158.90
Purchase #4	$121.71	4.246%	$126.8778	$126.88	$126.90	$126.90
Purchase #5	$7.49	3.283%	$7.7359	$7.74	$7.75	$7.70
Purchase #6	$38.92	3.475%	$40.2725	$40.27	$40.25	$40.30
Purchase #7	$58.39	11.673%	$65.2059	$65.21	$65.20	$65.20
7 purchase totals =	$672.84		$731.0458	$731.05	$731.05	$731.00