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	$162.47	13.146%	$183.8283	$183.83	$183.85	$183.80
Purchase #2	$116.96	12.110%	$131.1239	$131.12	$131.10	$131.10
Purchase #3	$151.58	13.556%	$172.1282	$172.13	$172.15	$172.10
Purchase #4	$19.99	3.687%	$20.727	$20.73	$20.75	$20.70
Purchase #5	$33.66	12.540%	$37.881	$37.88	$37.90	$37.90
Purchase #6	$46.84	8.721%	$50.9249	$50.92	$50.90	$50.90
Purchase #7	$55.86	13.683%	$63.5033	$63.50	$63.50	$63.50
7 purchase totals =	$587.36		$660.1166	$660.11	$660.15	$660.00