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	$158.91	6.268%	$168.8705	$168.87	$168.85	$168.90
Purchase #2	$121.63	13.105%	$137.5696	$137.57	$137.55	$137.60
Purchase #3	$60.42	11.642%	$67.4541	$67.45	$67.45	$67.50
Purchase #4	$61.29	6.707%	$65.4007	$65.40	$65.40	$65.40
Purchase #5	$151.57	7.492%	$162.9256	$162.93	$162.95	$162.90
Purchase #6	$126.36	3.238%	$130.4515	$130.45	$130.45	$130.50
Purchase #7	$64.92	13.713%	$73.8225	$73.82	$73.80	$73.80
7 purchase totals =	$745.10		$806.4945	$806.49	$806.45	$806.60