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	$59.60	13.127%	$67.4237	$67.42	$67.40	$67.40
Purchase #2	$36.99	10.451%	$40.8558	$40.86	$40.85	$40.90
Purchase #3	$103.75	7.370%	$111.3964	$111.40	$111.40	$111.40
Purchase #4	$103.74	8.198%	$112.2446	$112.24	$112.25	$112.20
Purchase #5	$12.47	11.800%	$13.9415	$13.94	$13.95	$13.90
Purchase #6	$123.80	6.536%	$131.8916	$131.89	$131.90	$131.90
Purchase #7	$194.31	3.562%	$201.2313	$201.23	$201.25	$201.20
7 purchase totals =	$634.66		$678.9849	$678.98	$679.00	$678.90