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	$184.47	5.311%	$194.2672	$194.27	$194.25	$194.30
Purchase #2	$142.53	7.293%	$152.9247	$152.92	$152.90	$152.90
Purchase #3	$126.52	12.781%	$142.6905	$142.69	$142.70	$142.70
Purchase #4	$19.64	11.873%	$21.9719	$21.97	$21.95	$22.00
Purchase #5	$106.96	4.337%	$111.5989	$111.60	$111.60	$111.60
Purchase #6	$24.29	12.348%	$27.2893	$27.29	$27.30	$27.30
Purchase #7	$27.92	4.639%	$29.2152	$29.22	$29.20	$29.20
7 purchase totals =	$632.33		$679.9577	$679.96	$679.90	$680.00