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	$54.91	4.291%	$57.2662	$57.27	$57.25	$57.30
Purchase #2	$116.76	6.136%	$123.9244	$123.92	$123.90	$123.90
Purchase #3	$19.93	3.685%	$20.6644	$20.66	$20.65	$20.70
Purchase #4	$207.29	11.510%	$231.1491	$231.15	$231.15	$231.10
Purchase #5	$55.89	7.410%	$60.0314	$60.03	$60.05	$60.00
Purchase #6	$18.70	5.826%	$19.7895	$19.79	$19.80	$19.80
Purchase #7	$129.71	13.782%	$147.5866	$147.59	$147.60	$147.60
7 purchase totals =	$603.19		$660.4116	$660.41	$660.40	$660.40