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	$166.96	3.428%	$172.6834	$172.68	$172.70	$172.70
Purchase #2	$63.61	9.741%	$69.8063	$69.81	$69.80	$69.80
Purchase #3	$26.42	10.390%	$29.165	$29.17	$29.15	$29.20
Purchase #4	$152.74	10.520%	$168.8082	$168.81	$168.80	$168.80
Purchase #5	$142.69	11.390%	$158.9424	$158.94	$158.95	$158.90
Purchase #6	$178.52	5.811%	$188.8938	$188.89	$188.90	$188.90
Purchase #7	$49.46	9.551%	$54.1839	$54.18	$54.20	$54.20
7 purchase totals =	$780.40		$842.4830	$842.48	$842.50	$842.50