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	$78.74	3.371%	$81.3943	$81.39	$81.40	$81.40
Purchase #2	$60.66	6.650%	$64.6939	$64.69	$64.70	$64.70
Purchase #3	$241.87	10.141%	$266.398	$266.40	$266.40	$266.40
Purchase #4	$120.36	13.622%	$136.7554	$136.76	$136.75	$136.80
Purchase #5	$53.44	4.472%	$55.8298	$55.83	$55.85	$55.80
Purchase #6	$40.93	4.169%	$42.6364	$42.64	$42.65	$42.60
Purchase #7	$79.64	11.561%	$88.8472	$88.85	$88.85	$88.80
7 purchase totals =	$675.64		$736.5550	$736.56	$736.60	$736.50