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	$149.89	4.515%	$156.6575	$156.66	$156.65	$156.70
Purchase #2	$216.66	10.523%	$239.4591	$239.46	$239.45	$239.50
Purchase #3	$142.39	3.707%	$147.6684	$147.67	$147.65	$147.70
Purchase #4	$65.78	7.283%	$70.5708	$70.57	$70.55	$70.60
Purchase #5	$111.45	10.638%	$123.3061	$123.31	$123.30	$123.30
Purchase #6	$9.65	4.209%	$10.0562	$10.06	$10.05	$10.10
Purchase #7	$128.77	9.612%	$141.1474	$141.15	$141.15	$141.10
7 purchase totals =	$824.59		$888.8655	$888.88	$888.80	$889.00