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	$206.27	10.374%	$227.6684	$227.67	$227.65	$227.70
Purchase #2	$111.59	11.761%	$124.7141	$124.71	$124.70	$124.70
Purchase #3	$221.74	8.103%	$239.7076	$239.71	$239.70	$239.70
Purchase #4	$192.34	9.853%	$211.2913	$211.29	$211.30	$211.30
Purchase #5	$176.95	7.762%	$190.6849	$190.68	$190.70	$190.70
Purchase #6	$6.42	12.423%	$7.2176	$7.22	$7.20	$7.20
Purchase #7	$87.91	13.244%	$99.5528	$99.55	$99.55	$99.60
7 purchase totals =	$1,003.22		$1,100.8367	$1,100.83	$1,100.80	$1,100.90