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	$87.43	4.749%	$91.5821	$91.58	$91.60	$91.60
Purchase #2	$97.94	9.752%	$107.4911	$107.49	$107.50	$107.50
Purchase #3	$99.55	11.169%	$110.6687	$110.67	$110.65	$110.70
Purchase #4	$169.42	9.292%	$185.1625	$185.16	$185.15	$185.20
Purchase #5	$77.97	13.240%	$88.2932	$88.29	$88.30	$88.30
Purchase #6	$57.73	3.308%	$59.6397	$59.64	$59.65	$59.60
Purchase #7	$42.54	6.298%	$45.2192	$45.22	$45.20	$45.20
7 purchase totals =	$632.58		$688.0565	$688.05	$688.05	$688.10