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	$156.89	13.548%	$178.1455	$178.15	$178.15	$178.10
Purchase #2	$185.74	10.304%	$204.8786	$204.88	$204.90	$204.90
Purchase #3	$237.67	8.819%	$258.6301	$258.63	$258.65	$258.60
Purchase #4	$122.32	6.489%	$130.2573	$130.26	$130.25	$130.30
Purchase #5	$210.50	3.866%	$218.6379	$218.64	$218.65	$218.60
Purchase #6	$114.61	11.278%	$127.5357	$127.54	$127.55	$127.50
Purchase #7	$95.50	8.160%	$103.2928	$103.29	$103.30	$103.30
7 purchase totals =	$1,123.23		$1,221.3779	$1,221.39	$1,221.45	$1,221.30