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	$155.81	7.247%	$167.1016	$167.10	$167.10	$167.10
Purchase #2	$247.97	7.212%	$265.8536	$265.85	$265.85	$265.90
Purchase #3	$22.30	11.260%	$24.811	$24.81	$24.80	$24.80
Purchase #4	$93.25	6.795%	$99.5863	$99.59	$99.60	$99.60
Purchase #5	$126.52	4.187%	$131.8174	$131.82	$131.80	$131.80
Purchase #6	$36.74	7.240%	$39.4	$39.40	$39.40	$39.40
Purchase #7	$230.93	13.200%	$261.4128	$261.41	$261.40	$261.40
7 purchase totals =	$913.52		$989.9827	$989.98	$989.95	$990.00