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	$21.43	5.601%	$22.6303	$22.63	$22.65	$22.60
Purchase #2	$110.25	10.639%	$121.9795	$121.98	$122.00	$122.00
Purchase #3	$49.38	3.605%	$51.1601	$51.16	$51.15	$51.20
Purchase #4	$31.37	4.840%	$32.8883	$32.89	$32.90	$32.90
Purchase #5	$34.54	3.841%	$35.8667	$35.87	$35.85	$35.90
Purchase #6	$176.72	6.443%	$188.1061	$188.11	$188.10	$188.10
Purchase #7	$66.83	8.249%	$72.3428	$72.34	$72.35	$72.30
7 purchase totals =	$490.52		$524.9738	$524.98	$525.00	$525.00