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	$132.70	11.176%	$147.5306	$147.53	$147.55	$147.50
Purchase #2	$105.61	13.401%	$119.7628	$119.76	$119.75	$119.80
Purchase #3	$38.42	3.354%	$39.7086	$39.71	$39.70	$39.70
Purchase #4	$74.94	6.462%	$79.7826	$79.78	$79.80	$79.80
Purchase #5	$51.81	3.827%	$53.7928	$53.79	$53.80	$53.80
Purchase #6	$197.47	5.846%	$209.0141	$209.01	$209.00	$209.00
Purchase #7	$17.30	3.685%	$17.9375	$17.94	$17.95	$17.90
7 purchase totals =	$618.25		$667.5290	$667.52	$667.55	$667.50