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	$150.63	11.172%	$167.4584	$167.46	$167.45	$167.50
Purchase #2	$208.92	5.184%	$219.7504	$219.75	$219.75	$219.80
Purchase #3	$90.77	9.219%	$99.1381	$99.14	$99.15	$99.10
Purchase #4	$128.66	10.152%	$141.7216	$141.72	$141.70	$141.70
Purchase #5	$237.46	10.647%	$262.7424	$262.74	$262.75	$262.70
Purchase #6	$55.98	9.303%	$61.1878	$61.19	$61.20	$61.20
Purchase #7	$130.39	13.378%	$147.8336	$147.83	$147.85	$147.80
7 purchase totals =	$1,002.81		$1,099.8323	$1,099.83	$1,099.85	$1,099.80