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	$16.65	6.786%	$17.7799	$17.78	$17.80	$17.80
Purchase #2	$56.40	8.766%	$61.344	$61.34	$61.35	$61.30
Purchase #3	$55.46	11.816%	$62.0132	$62.01	$62.00	$62.00
Purchase #4	$86.65	3.536%	$89.7139	$89.71	$89.70	$89.70
Purchase #5	$13.68	4.595%	$14.3086	$14.31	$14.30	$14.30
Purchase #6	$151.86	3.625%	$157.3649	$157.36	$157.35	$157.40
Purchase #7	$59.82	9.556%	$65.5364	$65.54	$65.55	$65.50
7 purchase totals =	$440.52		$468.0609	$468.05	$468.05	$468.00