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	$172.71	6.646%	$184.1883	$184.19	$184.20	$184.20
Purchase #2	$64.97	10.427%	$71.7444	$71.74	$71.75	$71.70
Purchase #3	$19.83	6.677%	$21.154	$21.15	$21.15	$21.20
Purchase #4	$154.97	11.176%	$172.2894	$172.29	$172.30	$172.30
Purchase #5	$66.40	8.289%	$71.9039	$71.90	$71.90	$71.90
Purchase #6	$37.71	13.246%	$42.7051	$42.71	$42.70	$42.70
Purchase #7	$231.95	3.695%	$240.5206	$240.52	$240.50	$240.50
7 purchase totals =	$748.54		$804.5057	$804.50	$804.50	$804.50