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	$200.40	11.531%	$223.5081	$223.51	$223.50	$223.50
Purchase #2	$148.27	6.350%	$157.6851	$157.69	$157.70	$157.70
Purchase #3	$205.79	4.701%	$215.4642	$215.46	$215.45	$215.50
Purchase #4	$134.94	11.281%	$150.1626	$150.16	$150.15	$150.20
Purchase #5	$172.41	3.267%	$178.0426	$178.04	$178.05	$178.00
Purchase #6	$36.37	7.838%	$39.2207	$39.22	$39.20	$39.20
Purchase #7	$227.49	13.789%	$258.8586	$258.86	$258.85	$258.90
7 purchase totals =	$1,125.67		$1,222.9419	$1,222.94	$1,222.90	$1,223.00