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	$76.45	9.277%	$83.5423	$83.54	$83.55	$83.50
Purchase #2	$5.71	5.167%	$6.005	$6.01	$6.00	$6.00
Purchase #3	$131.59	11.341%	$146.5136	$146.51	$146.50	$146.50
Purchase #4	$78.66	9.516%	$86.1453	$86.15	$86.15	$86.10
Purchase #5	$128.62	4.200%	$134.022	$134.02	$134.00	$134.00
Purchase #6	$9.73	8.711%	$10.5776	$10.58	$10.60	$10.60
Purchase #7	$56.46	13.443%	$64.0499	$64.05	$64.05	$64.00
7 purchase totals =	$487.22		$530.8557	$530.86	$530.85	$530.70