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	$130.36	12.391%	$146.5129	$146.51	$146.50	$146.50
Purchase #2	$39.26	12.808%	$44.2884	$44.29	$44.30	$44.30
Purchase #3	$89.78	13.195%	$101.6265	$101.63	$101.65	$101.60
Purchase #4	$34.68	3.393%	$35.8567	$35.86	$35.85	$35.90
Purchase #5	$32.60	5.599%	$34.4253	$34.43	$34.45	$34.40
Purchase #6	$152.73	12.574%	$171.9343	$171.93	$171.95	$171.90
Purchase #7	$123.31	3.317%	$127.4002	$127.40	$127.40	$127.40
7 purchase totals =	$602.72		$662.0443	$662.05	$662.10	$662.00