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	$45.84	8.764%	$49.8574	$49.86	$49.85	$49.90
Purchase #2	$149.56	13.314%	$169.4724	$169.47	$169.45	$169.50
Purchase #3	$113.44	7.219%	$121.6292	$121.63	$121.65	$121.60
Purchase #4	$109.35	12.845%	$123.396	$123.40	$123.40	$123.40
Purchase #5	$155.38	10.725%	$172.0445	$172.04	$172.05	$172.00
Purchase #6	$20.67	10.854%	$22.9135	$22.91	$22.90	$22.90
Purchase #7	$54.58	12.223%	$61.2513	$61.25	$61.25	$61.30
7 purchase totals =	$648.82		$720.5643	$720.56	$720.55	$720.60