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	$80.84	10.846%	$89.6079	$89.61	$89.60	$89.60
Purchase #2	$15.40	11.110%	$17.1109	$17.11	$17.10	$17.10
Purchase #3	$122.51	11.412%	$136.4908	$136.49	$136.50	$136.50
Purchase #4	$126.38	5.165%	$132.9075	$132.91	$132.90	$132.90
Purchase #5	$18.31	8.709%	$19.9046	$19.90	$19.90	$19.90
Purchase #6	$130.33	11.711%	$145.5929	$145.59	$145.60	$145.60
Purchase #7	$79.25	10.828%	$87.8312	$87.83	$87.85	$87.80
7 purchase totals =	$573.02		$629.4458	$629.44	$629.45	$629.40