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	$70.68	11.117%	$78.5375	$78.54	$78.55	$78.50
Purchase #2	$139.34	3.104%	$143.6651	$143.67	$143.65	$143.70
Purchase #3	$131.76	5.151%	$138.547	$138.55	$138.55	$138.50
Purchase #4	$238.62	8.784%	$259.5804	$259.58	$259.60	$259.60
Purchase #5	$23.75	5.170%	$24.9779	$24.98	$25.00	$25.00
Purchase #6	$238.29	4.331%	$248.6103	$248.61	$248.60	$248.60
Purchase #7	$197.34	4.756%	$206.7255	$206.73	$206.75	$206.70
7 purchase totals =	$1,039.78		$1,100.6437	$1,100.66	$1,100.70	$1,100.60