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	$99.50	12.455%	$111.8927	$111.89	$111.90	$111.90
Purchase #2	$138.66	5.692%	$146.5525	$146.55	$146.55	$146.60
Purchase #3	$153.37	8.577%	$166.5245	$166.52	$166.50	$166.50
Purchase #4	$206.38	6.795%	$220.4035	$220.40	$220.40	$220.40
Purchase #5	$163.59	4.204%	$170.4673	$170.47	$170.45	$170.50
Purchase #6	$68.59	9.581%	$75.1616	$75.16	$75.15	$75.20
Purchase #7	$222.67	9.537%	$243.906	$243.91	$243.90	$243.90
7 purchase totals =	$1,052.76		$1,134.9081	$1,134.90	$1,134.85	$1,135.00