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	$20.52	3.475%	$21.2331	$21.23	$21.25	$21.20
Purchase #2	$66.60	8.801%	$72.4615	$72.46	$72.45	$72.50
Purchase #3	$157.41	8.854%	$171.3471	$171.35	$171.35	$171.30
Purchase #4	$158.28	3.185%	$163.3212	$163.32	$163.30	$163.30
Purchase #5	$41.30	9.411%	$45.1867	$45.19	$45.20	$45.20
Purchase #6	$162.47	6.772%	$173.4725	$173.47	$173.45	$173.50
Purchase #7	$217.56	4.853%	$228.1182	$228.12	$228.10	$228.10
7 purchase totals =	$824.14		$875.1403	$875.14	$875.10	$875.10