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	$96.48	12.285%	$108.3326	$108.33	$108.35	$108.30
Purchase #2	$169.35	12.298%	$190.1767	$190.18	$190.20	$190.20
Purchase #3	$249.28	5.129%	$262.0656	$262.07	$262.05	$262.10
Purchase #4	$57.60	3.593%	$59.6696	$59.67	$59.65	$59.70
Purchase #5	$155.50	6.747%	$165.9916	$165.99	$166.00	$166.00
Purchase #6	$105.84	5.471%	$111.6305	$111.63	$111.65	$111.60
Purchase #7	$179.49	3.602%	$185.9552	$185.96	$185.95	$186.00
7 purchase totals =	$1,013.54		$1,083.8218	$1,083.83	$1,083.85	$1,083.90