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	$105.60	12.453%	$118.7504	$118.75	$118.75	$118.80
Purchase #2	$156.53	5.813%	$165.6291	$165.63	$165.65	$165.60
Purchase #3	$231.35	8.294%	$250.5382	$250.54	$250.55	$250.50
Purchase #4	$113.96	11.505%	$127.0711	$127.07	$127.05	$127.10
Purchase #5	$130.34	8.305%	$141.1647	$141.16	$141.15	$141.20
Purchase #6	$9.36	8.252%	$10.1324	$10.13	$10.15	$10.10
Purchase #7	$19.59	10.369%	$21.6213	$21.62	$21.60	$21.60
7 purchase totals =	$766.73		$834.9072	$834.90	$834.90	$834.90