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	$27.38	13.398%	$31.0484	$31.05	$31.05	$31.00
Purchase #2	$154.82	9.759%	$169.9289	$169.93	$169.95	$169.90
Purchase #3	$230.57	11.420%	$256.9011	$256.90	$256.90	$256.90
Purchase #4	$21.65	3.322%	$22.3692	$22.37	$22.35	$22.40
Purchase #5	$143.67	10.267%	$158.4206	$158.42	$158.40	$158.40
Purchase #6	$20.95	6.603%	$22.3333	$22.33	$22.35	$22.30
Purchase #7	$76.93	6.801%	$82.162	$82.16	$82.15	$82.20
7 purchase totals =	$675.97		$743.1635	$743.16	$743.15	$743.10