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	$36.79	10.869%	$40.7887	$40.79	$40.80	$40.80
Purchase #2	$97.44	12.585%	$109.7028	$109.70	$109.70	$109.70
Purchase #3	$168.96	5.448%	$178.1649	$178.16	$178.15	$178.20
Purchase #4	$176.51	7.555%	$189.8453	$189.85	$189.85	$189.80
Purchase #5	$87.77	9.761%	$96.3372	$96.34	$96.35	$96.30
Purchase #6	$103.67	7.406%	$111.3478	$111.35	$111.35	$111.30
Purchase #7	$17.32	7.504%	$18.6197	$18.62	$18.60	$18.60
7 purchase totals =	$688.46		$744.8064	$744.81	$744.80	$744.70