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	$26.40	13.405%	$29.9389	$29.94	$29.95	$29.90
Purchase #2	$40.78	4.654%	$42.6779	$42.68	$42.70	$42.70
Purchase #3	$249.89	11.758%	$279.2721	$279.27	$279.25	$279.30
Purchase #4	$35.53	4.517%	$37.1349	$37.13	$37.15	$37.10
Purchase #5	$162.95	12.666%	$183.5892	$183.59	$183.60	$183.60
Purchase #6	$134.65	3.318%	$139.1177	$139.12	$139.10	$139.10
Purchase #7	$59.37	3.865%	$61.6647	$61.66	$61.65	$61.70
7 purchase totals =	$709.57		$773.3954	$773.39	$773.40	$773.40