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	$60.42	9.334%	$66.0596	$66.06	$66.05	$66.10
Purchase #2	$141.59	7.104%	$151.6486	$151.65	$151.65	$151.60
Purchase #3	$228.50	6.801%	$244.0403	$244.04	$244.05	$244.00
Purchase #4	$48.41	5.689%	$51.164	$51.16	$51.15	$51.20
Purchase #5	$166.34	8.641%	$180.7134	$180.71	$180.70	$180.70
Purchase #6	$146.88	10.804%	$162.7489	$162.75	$162.75	$162.70
Purchase #7	$65.33	10.413%	$72.1328	$72.13	$72.15	$72.10
7 purchase totals =	$857.47		$928.5076	$928.50	$928.50	$928.40