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	$115.91	6.204%	$123.1011	$123.10	$123.10	$123.10
Purchase #2	$10.94	11.401%	$12.1873	$12.19	$12.20	$12.20
Purchase #3	$173.51	3.167%	$179.0051	$179.01	$179.00	$179.00
Purchase #4	$54.99	4.517%	$57.4739	$57.47	$57.45	$57.50
Purchase #5	$76.31	7.303%	$81.8829	$81.88	$81.90	$81.90
Purchase #6	$175.37	11.837%	$196.1285	$196.13	$196.15	$196.10
Purchase #7	$43.87	13.815%	$49.9306	$49.93	$49.95	$49.90
7 purchase totals =	$650.90		$699.7094	$699.71	$699.75	$699.70