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	$147.76	11.756%	$165.1307	$165.13	$165.15	$165.10
Purchase #2	$208.38	4.621%	$218.0092	$218.01	$218.00	$218.00
Purchase #3	$144.88	7.307%	$155.4664	$155.47	$155.45	$155.50
Purchase #4	$97.73	4.246%	$101.8796	$101.88	$101.90	$101.90
Purchase #5	$138.60	3.677%	$143.6963	$143.70	$143.70	$143.70
Purchase #6	$67.68	4.153%	$70.4908	$70.49	$70.50	$70.50
Purchase #7	$44.30	13.240%	$50.1653	$50.17	$50.15	$50.20
7 purchase totals =	$849.33		$904.8383	$904.85	$904.85	$904.90