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	$168.57	12.742%	$190.0492	$190.05	$190.05	$190.00
Purchase #2	$164.59	12.312%	$184.8543	$184.85	$184.85	$184.90
Purchase #3	$101.94	7.693%	$109.7822	$109.78	$109.80	$109.80
Purchase #4	$59.59	13.231%	$67.4744	$67.47	$67.45	$67.50
Purchase #5	$95.32	5.653%	$100.7084	$100.71	$100.70	$100.70
Purchase #6	$11.85	8.548%	$12.8629	$12.86	$12.85	$12.90
Purchase #7	$239.29	4.708%	$250.5558	$250.56	$250.55	$250.60
7 purchase totals =	$841.15		$916.2872	$916.28	$916.25	$916.40