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	$166.82	12.348%	$187.4189	$187.42	$187.40	$187.40
Purchase #2	$152.45	9.470%	$166.887	$166.89	$166.90	$166.90
Purchase #3	$185.57	10.209%	$204.5148	$204.51	$204.50	$204.50
Purchase #4	$70.93	12.754%	$79.9764	$79.98	$80.00	$80.00
Purchase #5	$92.90	13.178%	$105.1424	$105.14	$105.15	$105.10
Purchase #6	$43.71	13.448%	$49.5881	$49.59	$49.60	$49.60
Purchase #7	$203.78	6.319%	$216.6569	$216.66	$216.65	$216.70
7 purchase totals =	$916.16		$1,010.1845	$1,010.19	$1,010.20	$1,010.20