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	$106.43	13.152%	$120.4277	$120.43	$120.45	$120.40
Purchase #2	$64.53	13.261%	$73.0873	$73.09	$73.10	$73.10
Purchase #3	$16.62	13.503%	$18.8642	$18.86	$18.85	$18.90
Purchase #4	$160.94	12.209%	$180.5892	$180.59	$180.60	$180.60
Purchase #5	$152.94	5.144%	$160.8072	$160.81	$160.80	$160.80
Purchase #6	$106.35	4.499%	$111.1347	$111.13	$111.15	$111.10
Purchase #7	$6.29	8.195%	$6.8055	$6.81	$6.80	$6.80
7 purchase totals =	$614.10		$671.7158	$671.72	$671.75	$671.70