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	$26.31	9.811%	$28.8913	$28.89	$28.90	$28.90
Purchase #2	$60.60	10.144%	$66.7473	$66.75	$66.75	$66.70
Purchase #3	$239.99	10.508%	$265.2081	$265.21	$265.20	$265.20
Purchase #4	$20.88	3.500%	$21.6108	$21.61	$21.60	$21.60
Purchase #5	$157.37	9.746%	$172.7073	$172.71	$172.70	$172.70
Purchase #6	$88.37	13.818%	$100.581	$100.58	$100.60	$100.60
Purchase #7	$246.87	12.316%	$277.2745	$277.27	$277.25	$277.30
7 purchase totals =	$840.39		$933.0203	$933.02	$933.00	$933.00