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	$90.56	10.809%	$100.3486	$100.35	$100.35	$100.30
Purchase #2	$132.67	10.147%	$146.132	$146.13	$146.15	$146.10
Purchase #3	$184.90	3.126%	$190.68	$190.68	$190.70	$190.70
Purchase #4	$100.45	11.628%	$112.1303	$112.13	$112.15	$112.10
Purchase #5	$92.67	10.819%	$102.696	$102.70	$102.70	$102.70
Purchase #6	$66.54	10.138%	$73.2858	$73.29	$73.30	$73.30
Purchase #7	$235.63	5.629%	$248.8936	$248.89	$248.90	$248.90
7 purchase totals =	$903.42		$974.1663	$974.17	$974.25	$974.10