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	$108.89	13.506%	$123.5967	$123.60	$123.60	$123.60
Purchase #2	$109.47	13.192%	$123.9113	$123.91	$123.90	$123.90
Purchase #3	$153.41	10.768%	$169.9292	$169.93	$169.95	$169.90
Purchase #4	$77.86	7.720%	$83.8708	$83.87	$83.85	$83.90
Purchase #5	$131.41	9.763%	$144.2396	$144.24	$144.25	$144.20
Purchase #6	$155.70	12.525%	$175.2014	$175.20	$175.20	$175.20
Purchase #7	$157.77	8.653%	$171.4218	$171.42	$171.40	$171.40
7 purchase totals =	$894.51		$992.1708	$992.17	$992.15	$992.10