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	$20.42	3.708%	$21.1772	$21.18	$21.20	$21.20
Purchase #2	$210.94	3.475%	$218.2702	$218.27	$218.25	$218.30
Purchase #3	$149.75	8.361%	$162.2706	$162.27	$162.25	$162.30
Purchase #4	$23.40	6.325%	$24.8801	$24.88	$24.90	$24.90
Purchase #5	$36.94	5.348%	$38.9156	$38.92	$38.90	$38.90
Purchase #6	$132.29	13.507%	$150.1584	$150.16	$150.15	$150.20
Purchase #7	$111.85	7.167%	$119.8663	$119.87	$119.85	$119.90
7 purchase totals =	$685.59		$735.5384	$735.55	$735.50	$735.70