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	$96.98	3.509%	$100.383	$100.38	$100.40	$100.40
Purchase #2	$157.86	9.177%	$172.3468	$172.35	$172.35	$172.30
Purchase #3	$238.79	5.216%	$251.2453	$251.25	$251.25	$251.20
Purchase #4	$141.85	4.236%	$147.8588	$147.86	$147.85	$147.90
Purchase #5	$16.28	13.612%	$18.496	$18.50	$18.50	$18.50
Purchase #6	$57.88	5.648%	$61.1491	$61.15	$61.15	$61.10
Purchase #7	$44.94	11.405%	$50.0654	$50.07	$50.05	$50.10
7 purchase totals =	$754.58		$801.5444	$801.56	$801.55	$801.50