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	$13.43	11.733%	$15.0057	$15.01	$15.00	$15.00
Purchase #2	$127.30	6.811%	$135.9704	$135.97	$135.95	$136.00
Purchase #3	$96.38	7.404%	$103.516	$103.52	$103.50	$103.50
Purchase #4	$183.52	9.115%	$200.2478	$200.25	$200.25	$200.20
Purchase #5	$60.46	11.403%	$67.3543	$67.35	$67.35	$67.40
Purchase #6	$92.39	5.393%	$97.3726	$97.37	$97.35	$97.40
Purchase #7	$29.90	13.122%	$33.8235	$33.82	$33.80	$33.80
7 purchase totals =	$603.38		$653.2903	$653.29	$653.20	$653.30