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	$83.72	6.476%	$89.1417	$89.14	$89.15	$89.10
Purchase #2	$167.75	9.385%	$183.4933	$183.49	$183.50	$183.50
Purchase #3	$145.52	10.662%	$161.0353	$161.04	$161.05	$161.00
Purchase #4	$34.76	6.685%	$37.0837	$37.08	$37.10	$37.10
Purchase #5	$242.25	13.680%	$275.3898	$275.39	$275.40	$275.40
Purchase #6	$207.64	4.420%	$216.8177	$216.82	$216.80	$216.80
Purchase #7	$216.73	9.440%	$237.1893	$237.19	$237.20	$237.20
7 purchase totals =	$1,098.37		$1,200.1508	$1,200.15	$1,200.20	$1,200.10