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	$14.59	6.177%	$15.4912	$15.49	$15.50	$15.50
Purchase #2	$154.46	6.484%	$164.4752	$164.48	$164.50	$164.50
Purchase #3	$50.34	8.255%	$54.4956	$54.50	$54.50	$54.50
Purchase #4	$154.54	5.381%	$162.8558	$162.86	$162.85	$162.90
Purchase #5	$233.51	6.583%	$248.882	$248.88	$248.90	$248.90
Purchase #6	$16.61	9.835%	$18.2436	$18.24	$18.25	$18.20
Purchase #7	$61.42	5.166%	$64.593	$64.59	$64.60	$64.60
7 purchase totals =	$685.47		$729.0364	$729.04	$729.10	$729.10