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	$34.59	12.445%	$38.8947	$38.89	$38.90	$38.90
Purchase #2	$93.37	6.824%	$99.7416	$99.74	$99.75	$99.70
Purchase #3	$248.72	9.569%	$272.52	$272.52	$272.50	$272.50
Purchase #4	$9.39	13.496%	$10.6573	$10.66	$10.65	$10.70
Purchase #5	$90.70	11.141%	$100.8049	$100.80	$100.80	$100.80
Purchase #6	$210.74	10.427%	$232.7139	$232.71	$232.70	$232.70
Purchase #7	$151.76	7.338%	$162.8961	$162.90	$162.90	$162.90
7 purchase totals =	$839.27		$918.2285	$918.22	$918.20	$918.20