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	$74.64	12.766%	$84.1685	$84.17	$84.15	$84.20
Purchase #2	$52.89	8.507%	$57.3894	$57.39	$57.40	$57.40
Purchase #3	$58.72	12.449%	$66.0301	$66.03	$66.05	$66.00
Purchase #4	$146.60	4.337%	$152.958	$152.96	$152.95	$153.00
Purchase #5	$6.39	13.545%	$7.2555	$7.26	$7.25	$7.30
Purchase #6	$151.35	3.545%	$156.7154	$156.72	$156.70	$156.70
Purchase #7	$212.89	4.439%	$222.3402	$222.34	$222.35	$222.30
7 purchase totals =	$703.48		$746.8571	$746.87	$746.85	$746.90