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	$13.68	13.228%	$15.4896	$15.49	$15.50	$15.50
Purchase #2	$108.25	7.297%	$116.149	$116.15	$116.15	$116.10
Purchase #3	$120.75	8.788%	$131.3615	$131.36	$131.35	$131.40
Purchase #4	$135.82	11.263%	$151.1174	$151.12	$151.10	$151.10
Purchase #5	$73.63	3.814%	$76.4382	$76.44	$76.45	$76.40
Purchase #6	$89.51	12.505%	$100.7032	$100.70	$100.70	$100.70
Purchase #7	$249.64	10.254%	$275.2381	$275.24	$275.25	$275.20
7 purchase totals =	$791.28		$866.4970	$866.50	$866.50	$866.40