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	$69.28	12.229%	$77.7523	$77.75	$77.75	$77.80
Purchase #2	$91.38	3.504%	$94.582	$94.58	$94.60	$94.60
Purchase #3	$104.48	4.823%	$109.5191	$109.52	$109.50	$109.50
Purchase #4	$196.29	11.847%	$219.5445	$219.54	$219.55	$219.50
Purchase #5	$154.78	7.344%	$166.147	$166.15	$166.15	$166.10
Purchase #6	$144.89	11.495%	$161.5451	$161.55	$161.55	$161.50
Purchase #7	$77.71	4.588%	$81.2753	$81.28	$81.30	$81.30
7 purchase totals =	$838.81		$910.3653	$910.37	$910.40	$910.30