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	$121.68	8.152%	$131.5994	$131.60	$131.60	$131.60
Purchase #2	$59.68	12.110%	$66.9072	$66.91	$66.90	$66.90
Purchase #3	$150.71	11.418%	$167.9181	$167.92	$167.90	$167.90
Purchase #4	$132.89	8.269%	$143.8787	$143.88	$143.90	$143.90
Purchase #5	$172.96	10.165%	$190.5414	$190.54	$190.55	$190.50
Purchase #6	$20.55	4.452%	$21.4649	$21.46	$21.45	$21.50
Purchase #7	$94.69	9.848%	$104.0151	$104.02	$104.00	$104.00
7 purchase totals =	$753.16		$826.3248	$826.33	$826.30	$826.30