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	$32.81	10.218%	$36.1625	$36.16	$36.15	$36.20
Purchase #2	$50.93	10.769%	$56.4147	$56.41	$56.40	$56.40
Purchase #3	$74.30	11.409%	$82.7769	$82.78	$82.80	$82.80
Purchase #4	$76.88	6.620%	$81.9695	$81.97	$81.95	$82.00
Purchase #5	$133.68	8.455%	$144.9826	$144.98	$145.00	$145.00
Purchase #6	$50.83	5.208%	$53.4772	$53.48	$53.50	$53.50
Purchase #7	$115.97	6.356%	$123.3411	$123.34	$123.35	$123.30
7 purchase totals =	$535.40		$579.1245	$579.12	$579.15	$579.20