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	$39.43	4.130%	$41.0585	$41.06	$41.05	$41.10
Purchase #2	$150.73	4.312%	$157.2295	$157.23	$157.25	$157.20
Purchase #3	$19.92	11.171%	$22.1453	$22.15	$22.15	$22.10
Purchase #4	$98.65	4.601%	$103.1889	$103.19	$103.20	$103.20
Purchase #5	$106.55	11.221%	$118.506	$118.51	$118.50	$118.50
Purchase #6	$101.47	9.442%	$111.0508	$111.05	$111.05	$111.10
Purchase #7	$22.29	7.132%	$23.8797	$23.88	$23.90	$23.90
7 purchase totals =	$539.04		$577.0587	$577.07	$577.10	$577.10