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	$183.43	9.363%	$200.6046	$200.60	$200.60	$200.60
Purchase #2	$52.25	9.379%	$57.1505	$57.15	$57.15	$57.20
Purchase #3	$33.29	8.144%	$36.0011	$36.00	$36.00	$36.00
Purchase #4	$180.75	6.741%	$192.9344	$192.93	$192.95	$192.90
Purchase #5	$132.93	4.595%	$139.0381	$139.04	$139.05	$139.00
Purchase #6	$109.61	12.600%	$123.4209	$123.42	$123.40	$123.40
Purchase #7	$74.72	11.692%	$83.4563	$83.46	$83.45	$83.50
7 purchase totals =	$766.98		$832.6059	$832.60	$832.60	$832.60