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	$83.31	10.627%	$92.1634	$92.16	$92.15	$92.20
Purchase #2	$37.75	7.174%	$40.4582	$40.46	$40.45	$40.50
Purchase #3	$243.28	6.720%	$259.6284	$259.63	$259.65	$259.60
Purchase #4	$127.90	12.284%	$143.6112	$143.61	$143.60	$143.60
Purchase #5	$75.37	10.626%	$83.3788	$83.38	$83.40	$83.40
Purchase #6	$227.99	8.575%	$247.5401	$247.54	$247.55	$247.50
Purchase #7	$73.85	11.428%	$82.2896	$82.29	$82.30	$82.30
7 purchase totals =	$869.45		$949.0697	$949.07	$949.10	$949.10