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	$16.59	13.203%	$18.7804	$18.78	$18.80	$18.80
Purchase #2	$39.57	5.566%	$41.7725	$41.77	$41.75	$41.80
Purchase #3	$144.91	13.629%	$164.6598	$164.66	$164.65	$164.70
Purchase #4	$122.71	13.799%	$139.6428	$139.64	$139.65	$139.60
Purchase #5	$142.81	6.596%	$152.2297	$152.23	$152.25	$152.20
Purchase #6	$143.79	10.306%	$158.609	$158.61	$158.60	$158.60
Purchase #7	$109.62	9.301%	$119.8158	$119.82	$119.80	$119.80
7 purchase totals =	$720.00		$795.5100	$795.51	$795.50	$795.50