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	$125.99	8.354%	$136.5152	$136.52	$136.50	$136.50
Purchase #2	$77.28	7.804%	$83.3109	$83.31	$83.30	$83.30
Purchase #3	$240.38	6.320%	$255.572	$255.57	$255.55	$255.60
Purchase #4	$11.84	13.278%	$13.4121	$13.41	$13.40	$13.40
Purchase #5	$169.37	12.390%	$190.3549	$190.35	$190.35	$190.40
Purchase #6	$44.34	12.270%	$49.7805	$49.78	$49.80	$49.80
Purchase #7	$89.80	10.387%	$99.1275	$99.13	$99.15	$99.10
7 purchase totals =	$759.00		$828.0731	$828.07	$828.05	$828.10