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	$153.53	7.661%	$165.2919	$165.29	$165.30	$165.30
Purchase #2	$173.92	3.852%	$180.6194	$180.62	$180.60	$180.60
Purchase #3	$105.34	7.399%	$113.1341	$113.13	$113.15	$113.10
Purchase #4	$19.30	11.764%	$21.5705	$21.57	$21.55	$21.60
Purchase #5	$125.87	13.420%	$142.7618	$142.76	$142.75	$142.80
Purchase #6	$150.43	5.614%	$158.8751	$158.88	$158.90	$158.90
Purchase #7	$103.74	9.656%	$113.7571	$113.76	$113.75	$113.80
7 purchase totals =	$832.13		$896.0099	$896.01	$896.00	$896.10