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	$136.38	7.222%	$146.2294	$146.23	$146.25	$146.20
Purchase #2	$52.77	9.242%	$57.647	$57.65	$57.65	$57.60
Purchase #3	$46.54	4.433%	$48.6031	$48.60	$48.60	$48.60
Purchase #4	$163.80	10.635%	$181.2201	$181.22	$181.20	$181.20
Purchase #5	$39.56	3.520%	$40.9525	$40.95	$40.95	$41.00
Purchase #6	$85.82	8.260%	$92.9087	$92.91	$92.90	$92.90
Purchase #7	$36.78	9.776%	$40.3756	$40.38	$40.40	$40.40
7 purchase totals =	$561.65		$607.9364	$607.94	$607.95	$607.90