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	$56.76	6.198%	$60.278	$60.28	$60.30	$60.30
Purchase #2	$126.33	4.794%	$132.3863	$132.39	$132.40	$132.40
Purchase #3	$152.91	10.171%	$168.4625	$168.46	$168.45	$168.50
Purchase #4	$69.77	10.254%	$76.9242	$76.92	$76.90	$76.90
Purchase #5	$212.58	12.212%	$238.5403	$238.54	$238.55	$238.50
Purchase #6	$79.70	4.244%	$83.0825	$83.08	$83.10	$83.10
Purchase #7	$185.57	7.528%	$199.5397	$199.54	$199.55	$199.50
7 purchase totals =	$883.62		$959.2135	$959.21	$959.25	$959.20