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	$91.84	8.403%	$99.5573	$99.56	$99.55	$99.60
Purchase #2	$193.48	6.437%	$205.9343	$205.93	$205.95	$205.90
Purchase #3	$152.37	13.260%	$172.5743	$172.57	$172.55	$172.60
Purchase #4	$233.61	12.265%	$262.2623	$262.26	$262.25	$262.30
Purchase #5	$13.94	9.231%	$15.2268	$15.23	$15.25	$15.20
Purchase #6	$143.58	4.782%	$150.446	$150.45	$150.45	$150.40
Purchase #7	$49.64	7.338%	$53.2826	$53.28	$53.30	$53.30
7 purchase totals =	$878.46		$959.2836	$959.28	$959.30	$959.30