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	$112.38	9.517%	$123.0752	$123.08	$123.10	$123.10
Purchase #2	$5.38	3.329%	$5.5591	$5.56	$5.55	$5.60
Purchase #3	$240.54	7.363%	$258.251	$258.25	$258.25	$258.30
Purchase #4	$17.38	11.616%	$19.3989	$19.40	$19.40	$19.40
Purchase #5	$10.48	9.436%	$11.4689	$11.47	$11.45	$11.50
Purchase #6	$151.27	13.616%	$171.8669	$171.87	$171.85	$171.90
Purchase #7	$88.53	6.455%	$94.2446	$94.24	$94.25	$94.20
7 purchase totals =	$625.96		$683.8646	$683.87	$683.85	$684.00