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	$107.66	7.856%	$116.1178	$116.12	$116.10	$116.10
Purchase #2	$173.45	10.601%	$191.8374	$191.84	$191.85	$191.80
Purchase #3	$45.29	10.735%	$50.1519	$50.15	$50.15	$50.20
Purchase #4	$112.48	13.657%	$127.8414	$127.84	$127.85	$127.80
Purchase #5	$225.77	6.692%	$240.8785	$240.88	$240.90	$240.90
Purchase #6	$81.76	13.136%	$92.5	$92.50	$92.50	$92.50
Purchase #7	$156.49	3.105%	$161.349	$161.35	$161.35	$161.30
7 purchase totals =	$902.90		$980.6760	$980.68	$980.70	$980.60