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	$172.36	7.850%	$185.8903	$185.89	$185.90	$185.90
Purchase #2	$49.40	9.565%	$54.1251	$54.13	$54.15	$54.10
Purchase #3	$217.27	6.427%	$231.2339	$231.23	$231.25	$231.20
Purchase #4	$159.60	5.792%	$168.844	$168.84	$168.85	$168.80
Purchase #5	$154.61	10.594%	$170.9894	$170.99	$171.00	$171.00
Purchase #6	$93.27	3.467%	$96.5037	$96.50	$96.50	$96.50
Purchase #7	$165.64	4.803%	$173.5957	$173.60	$173.60	$173.60
7 purchase totals =	$1,012.15		$1,081.1821	$1,081.18	$1,081.25	$1,081.10