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	$79.69	3.807%	$82.7238	$82.72	$82.70	$82.70
Purchase #2	$29.95	12.592%	$33.7213	$33.72	$33.70	$33.70
Purchase #3	$109.96	13.603%	$124.9179	$124.92	$124.90	$124.90
Purchase #4	$134.47	8.166%	$145.4508	$145.45	$145.45	$145.50
Purchase #5	$94.71	6.280%	$100.6578	$100.66	$100.65	$100.70
Purchase #6	$237.92	11.457%	$265.1785	$265.18	$265.20	$265.20
Purchase #7	$205.93	10.210%	$226.9555	$226.96	$226.95	$227.00
7 purchase totals =	$892.63		$979.6056	$979.61	$979.55	$979.70