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	$70.87	10.523%	$78.3277	$78.33	$78.35	$78.30
Purchase #2	$17.89	3.253%	$18.472	$18.47	$18.45	$18.50
Purchase #3	$37.47	7.669%	$40.3436	$40.34	$40.35	$40.30
Purchase #4	$220.35	4.496%	$230.2569	$230.26	$230.25	$230.30
Purchase #5	$146.61	7.172%	$157.1249	$157.12	$157.10	$157.10
Purchase #6	$77.57	5.287%	$81.6711	$81.67	$81.65	$81.70
Purchase #7	$75.84	3.221%	$78.2828	$78.28	$78.30	$78.30
7 purchase totals =	$646.60		$684.4790	$684.47	$684.45	$684.50