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	$17.30	7.426%	$18.5847	$18.58	$18.60	$18.60
Purchase #2	$74.65	4.702%	$78.16	$78.16	$78.15	$78.20
Purchase #3	$162.63	12.138%	$182.37	$182.37	$182.35	$182.40
Purchase #4	$125.40	5.796%	$132.6682	$132.67	$132.65	$132.70
Purchase #5	$115.45	7.263%	$123.8351	$123.84	$123.85	$123.80
Purchase #6	$230.98	3.328%	$238.667	$238.67	$238.65	$238.70
Purchase #7	$157.61	6.253%	$167.4654	$167.47	$167.45	$167.50
7 purchase totals =	$884.02		$941.7504	$941.76	$941.70	$941.90