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	$91.69	9.705%	$100.5885	$100.59	$100.60	$100.60
Purchase #2	$178.95	4.189%	$186.4462	$186.45	$186.45	$186.40
Purchase #3	$139.89	10.705%	$154.8652	$154.87	$154.85	$154.90
Purchase #4	$62.67	8.731%	$68.1417	$68.14	$68.15	$68.10
Purchase #5	$146.90	5.748%	$155.3438	$155.34	$155.35	$155.30
Purchase #6	$10.69	7.314%	$11.4719	$11.47	$11.45	$11.50
Purchase #7	$123.56	4.762%	$129.4439	$129.44	$129.45	$129.40
7 purchase totals =	$754.35		$806.3012	$806.30	$806.30	$806.20