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	$170.82	7.864%	$184.2533	$184.25	$184.25	$184.30
Purchase #2	$144.93	6.664%	$154.5881	$154.59	$154.60	$154.60
Purchase #3	$124.87	12.838%	$140.9008	$140.90	$140.90	$140.90
Purchase #4	$73.87	10.142%	$81.3619	$81.36	$81.35	$81.40
Purchase #5	$146.34	9.210%	$159.8179	$159.82	$159.80	$159.80
Purchase #6	$79.92	13.732%	$90.8946	$90.89	$90.90	$90.90
Purchase #7	$208.69	11.741%	$233.1923	$233.19	$233.20	$233.20
7 purchase totals =	$949.44		$1,045.0089	$1,045.00	$1,045.00	$1,045.10