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	$124.92	6.239%	$132.7138	$132.71	$132.70	$132.70
Purchase #2	$96.52	4.633%	$100.9918	$100.99	$101.00	$101.00
Purchase #3	$37.72	13.602%	$42.8507	$42.85	$42.85	$42.90
Purchase #4	$220.43	8.217%	$238.5427	$238.54	$238.55	$238.50
Purchase #5	$80.85	10.653%	$89.463	$89.46	$89.45	$89.50
Purchase #6	$117.57	5.191%	$123.6731	$123.67	$123.65	$123.70
Purchase #7	$137.80	8.410%	$149.389	$149.39	$149.40	$149.40
7 purchase totals =	$815.81		$877.6241	$877.61	$877.60	$877.70