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	$130.70	6.389%	$139.0504	$139.05	$139.05	$139.10
Purchase #2	$151.88	4.446%	$158.6326	$158.63	$158.65	$158.60
Purchase #3	$94.34	6.855%	$100.807	$100.81	$100.80	$100.80
Purchase #4	$89.70	6.243%	$95.3	$95.30	$95.30	$95.30
Purchase #5	$75.27	4.239%	$78.4607	$78.46	$78.45	$78.50
Purchase #6	$131.54	11.272%	$146.3672	$146.37	$146.35	$146.40
Purchase #7	$43.65	13.349%	$49.4768	$49.48	$49.50	$49.50
7 purchase totals =	$717.08		$768.0947	$768.10	$768.10	$768.20