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	$112.53	7.681%	$121.1734	$121.17	$121.15	$121.20
Purchase #2	$237.53	6.392%	$252.7129	$252.71	$252.70	$252.70
Purchase #3	$26.46	7.558%	$28.4598	$28.46	$28.45	$28.50
Purchase #4	$219.28	13.169%	$248.157	$248.16	$248.15	$248.20
Purchase #5	$65.81	10.306%	$72.5924	$72.59	$72.60	$72.60
Purchase #6	$68.77	13.630%	$78.1434	$78.14	$78.15	$78.10
Purchase #7	$91.96	7.690%	$99.0317	$99.03	$99.05	$99.00
7 purchase totals =	$822.34		$900.2706	$900.26	$900.25	$900.30