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	$102.65	3.793%	$106.5435	$106.54	$106.55	$106.50
Purchase #2	$17.60	13.860%	$20.0394	$20.04	$20.05	$20.00
Purchase #3	$34.44	13.258%	$39.0061	$39.01	$39.00	$39.00
Purchase #4	$141.26	11.295%	$157.2153	$157.22	$157.20	$157.20
Purchase #5	$157.56	9.569%	$172.6369	$172.64	$172.65	$172.60
Purchase #6	$13.98	11.801%	$15.6298	$15.63	$15.65	$15.60
Purchase #7	$18.82	13.461%	$21.3534	$21.35	$21.35	$21.40
7 purchase totals =	$486.31		$532.4244	$532.43	$532.45	$532.30