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	$60.46	9.538%	$66.2267	$66.23	$66.25	$66.20
Purchase #2	$117.94	12.384%	$132.5457	$132.55	$132.55	$132.50
Purchase #3	$51.36	12.771%	$57.9192	$57.92	$57.90	$57.90
Purchase #4	$33.39	11.630%	$37.2733	$37.27	$37.25	$37.30
Purchase #5	$16.54	13.418%	$18.7593	$18.76	$18.75	$18.80
Purchase #6	$107.95	10.276%	$119.0429	$119.04	$119.05	$119.00
Purchase #7	$95.66	3.707%	$99.2061	$99.21	$99.20	$99.20
7 purchase totals =	$483.30		$530.9732	$530.98	$530.95	$530.90