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	$152.92	8.303%	$165.6169	$165.62	$165.60	$165.60
Purchase #2	$108.49	8.695%	$117.9232	$117.92	$117.90	$117.90
Purchase #3	$56.81	4.570%	$59.4062	$59.41	$59.40	$59.40
Purchase #4	$78.35	3.204%	$80.8603	$80.86	$80.85	$80.90
Purchase #5	$57.53	9.322%	$62.8929	$62.89	$62.90	$62.90
Purchase #6	$111.96	7.617%	$120.488	$120.49	$120.50	$120.50
Purchase #7	$189.44	13.624%	$215.2493	$215.25	$215.25	$215.20
7 purchase totals =	$755.50		$822.4368	$822.44	$822.40	$822.40