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	$166.38	11.378%	$185.3107	$185.31	$185.30	$185.30
Purchase #2	$63.68	4.148%	$66.3214	$66.32	$66.30	$66.30
Purchase #3	$60.41	11.125%	$67.1306	$67.13	$67.15	$67.10
Purchase #4	$158.43	5.515%	$167.1674	$167.17	$167.15	$167.20
Purchase #5	$201.76	4.121%	$210.0745	$210.07	$210.05	$210.10
Purchase #6	$158.59	8.194%	$171.5849	$171.58	$171.60	$171.60
Purchase #7	$127.83	9.532%	$140.0148	$140.01	$140.00	$140.00
7 purchase totals =	$937.08		$1,007.6043	$1,007.59	$1,007.55	$1,007.60