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	$33.66	12.570%	$37.8911	$37.89	$37.90	$37.90
Purchase #2	$71.33	11.798%	$79.7455	$79.75	$79.75	$79.70
Purchase #3	$60.73	9.190%	$66.3111	$66.31	$66.30	$66.30
Purchase #4	$22.47	8.337%	$24.3433	$24.34	$24.35	$24.30
Purchase #5	$239.29	8.187%	$258.8807	$258.88	$258.90	$258.90
Purchase #6	$191.56	13.602%	$217.616	$217.62	$217.60	$217.60
Purchase #7	$90.46	10.639%	$100.084	$100.08	$100.10	$100.10
7 purchase totals =	$709.50		$784.8717	$784.87	$784.90	$784.80