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	$89.56	11.830%	$100.1549	$100.15	$100.15	$100.20
Purchase #2	$200.80	13.617%	$228.1429	$228.14	$228.15	$228.10
Purchase #3	$33.82	10.397%	$37.3363	$37.34	$37.35	$37.30
Purchase #4	$76.62	12.696%	$86.3477	$86.35	$86.35	$86.30
Purchase #5	$192.33	11.509%	$214.4653	$214.47	$214.45	$214.50
Purchase #6	$67.78	8.490%	$73.5345	$73.53	$73.55	$73.50
Purchase #7	$30.67	11.827%	$34.2973	$34.30	$34.30	$34.30
7 purchase totals =	$691.58		$774.2789	$774.28	$774.30	$774.20