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	$134.48	5.601%	$142.0122	$142.01	$142.00	$142.00
Purchase #2	$187.43	4.838%	$196.4979	$196.50	$196.50	$196.50
Purchase #3	$234.40	8.397%	$254.0826	$254.08	$254.10	$254.10
Purchase #4	$97.62	11.577%	$108.9215	$108.92	$108.90	$108.90
Purchase #5	$134.69	8.767%	$146.4983	$146.50	$146.50	$146.50
Purchase #6	$16.81	13.703%	$19.1135	$19.11	$19.10	$19.10
Purchase #7	$40.95	5.722%	$43.2932	$43.29	$43.30	$43.30
7 purchase totals =	$846.38		$910.4192	$910.41	$910.40	$910.40