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	$186.70	12.771%	$210.5435	$210.54	$210.55	$210.50
Purchase #2	$19.64	6.160%	$20.8498	$20.85	$20.85	$20.80
Purchase #3	$24.92	8.445%	$27.0245	$27.02	$27.00	$27.00
Purchase #4	$34.61	9.311%	$37.8325	$37.83	$37.85	$37.80
Purchase #5	$93.96	10.476%	$103.8032	$103.80	$103.80	$103.80
Purchase #6	$142.49	9.250%	$155.6703	$155.67	$155.65	$155.70
Purchase #7	$13.73	7.851%	$14.8079	$14.81	$14.80	$14.80
7 purchase totals =	$516.05		$570.5317	$570.52	$570.50	$570.40