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	$7.54	13.647%	$8.569	$8.57	$8.55	$8.60
Purchase #2	$180.38	4.175%	$187.9109	$187.91	$187.90	$187.90
Purchase #3	$194.94	11.771%	$217.8864	$217.89	$217.90	$217.90
Purchase #4	$60.68	7.149%	$65.018	$65.02	$65.00	$65.00
Purchase #5	$123.59	13.365%	$140.1078	$140.11	$140.10	$140.10
Purchase #6	$57.29	7.841%	$61.7821	$61.78	$61.80	$61.80
Purchase #7	$137.49	9.228%	$150.1776	$150.18	$150.20	$150.20
7 purchase totals =	$761.91		$831.4518	$831.46	$831.45	$831.50