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	$158.98	9.261%	$173.7031	$173.70	$173.70	$173.70
Purchase #2	$46.80	12.203%	$52.511	$52.51	$52.50	$52.50
Purchase #3	$213.45	12.525%	$240.1846	$240.18	$240.20	$240.20
Purchase #4	$59.43	4.694%	$62.2196	$62.22	$62.20	$62.20
Purchase #5	$175.46	10.488%	$193.8622	$193.86	$193.85	$193.90
Purchase #6	$38.33	11.719%	$42.8219	$42.82	$42.80	$42.80
Purchase #7	$131.86	12.612%	$148.4902	$148.49	$148.50	$148.50
7 purchase totals =	$824.31		$913.7926	$913.78	$913.75	$913.80