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	$58.79	12.716%	$66.2657	$66.27	$66.25	$66.30
Purchase #2	$132.40	13.769%	$150.6302	$150.63	$150.65	$150.60
Purchase #3	$210.47	13.484%	$238.8498	$238.85	$238.85	$238.80
Purchase #4	$168.99	5.673%	$178.5768	$178.58	$178.60	$178.60
Purchase #5	$10.90	13.386%	$12.3591	$12.36	$12.35	$12.40
Purchase #6	$99.63	9.562%	$109.1566	$109.16	$109.15	$109.20
Purchase #7	$6.73	10.454%	$7.4336	$7.43	$7.45	$7.40
7 purchase totals =	$687.91		$763.2718	$763.28	$763.30	$763.30