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	$99.31	8.670%	$107.9202	$107.92	$107.90	$107.90
Purchase #2	$166.75	4.162%	$173.6901	$173.69	$173.70	$173.70
Purchase #3	$156.57	7.832%	$168.8326	$168.83	$168.85	$168.80
Purchase #4	$90.37	6.857%	$96.5667	$96.57	$96.55	$96.60
Purchase #5	$48.80	4.167%	$50.8335	$50.83	$50.85	$50.80
Purchase #6	$145.83	3.646%	$151.147	$151.15	$151.15	$151.10
Purchase #7	$90.91	4.675%	$95.16	$95.16	$95.15	$95.20
7 purchase totals =	$798.54		$844.1501	$844.15	$844.15	$844.10