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	$171.77	9.162%	$187.5076	$187.51	$187.50	$187.50
Purchase #2	$172.80	10.466%	$190.8852	$190.89	$190.90	$190.90
Purchase #3	$125.35	11.463%	$139.7189	$139.72	$139.70	$139.70
Purchase #4	$48.53	4.174%	$50.5556	$50.56	$50.55	$50.60
Purchase #5	$18.81	4.282%	$19.6154	$19.62	$19.60	$19.60
Purchase #6	$166.36	12.449%	$187.0702	$187.07	$187.05	$187.10
Purchase #7	$160.32	4.328%	$167.2586	$167.26	$167.25	$167.30
7 purchase totals =	$863.94		$942.6115	$942.63	$942.55	$942.70