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	$31.41	6.549%	$33.467	$33.47	$33.45	$33.50
Purchase #2	$22.78	7.749%	$24.5452	$24.55	$24.55	$24.50
Purchase #3	$247.59	3.641%	$256.6048	$256.60	$256.60	$256.60
Purchase #4	$111.60	5.425%	$117.6543	$117.65	$117.65	$117.70
Purchase #5	$143.48	11.507%	$159.9902	$159.99	$160.00	$160.00
Purchase #6	$39.29	5.638%	$41.5052	$41.51	$41.50	$41.50
Purchase #7	$83.87	10.811%	$92.9372	$92.94	$92.95	$92.90
7 purchase totals =	$680.02		$726.7039	$726.71	$726.70	$726.70