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	$115.95	6.749%	$123.7755	$123.78	$123.80	$123.80
Purchase #2	$148.32	13.551%	$168.4188	$168.42	$168.40	$168.40
Purchase #3	$12.74	5.128%	$13.3933	$13.39	$13.40	$13.40
Purchase #4	$34.27	9.436%	$37.5037	$37.50	$37.50	$37.50
Purchase #5	$135.32	3.801%	$140.4635	$140.46	$140.45	$140.50
Purchase #6	$53.33	13.777%	$60.6773	$60.68	$60.70	$60.70
Purchase #7	$65.72	12.318%	$73.8154	$73.82	$73.80	$73.80
7 purchase totals =	$565.65		$618.0475	$618.05	$618.05	$618.10