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	$187.78	10.324%	$207.1664	$207.17	$207.15	$207.20
Purchase #2	$52.47	11.530%	$58.5198	$58.52	$58.50	$58.50
Purchase #3	$140.87	7.801%	$151.8593	$151.86	$151.85	$151.90
Purchase #4	$94.97	8.862%	$103.3862	$103.39	$103.40	$103.40
Purchase #5	$57.62	3.156%	$59.4385	$59.44	$59.45	$59.40
Purchase #6	$235.94	8.455%	$255.8887	$255.89	$255.90	$255.90
Purchase #7	$19.70	4.848%	$20.6551	$20.66	$20.65	$20.70
7 purchase totals =	$789.35		$856.9140	$856.93	$856.90	$857.00