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	$19.38	5.511%	$20.448	$20.45	$20.45	$20.40
Purchase #2	$107.85	4.584%	$112.7938	$112.79	$112.80	$112.80
Purchase #3	$238.74	10.534%	$263.8889	$263.89	$263.90	$263.90
Purchase #4	$128.57	4.484%	$134.3351	$134.34	$134.35	$134.30
Purchase #5	$132.78	10.584%	$146.8334	$146.83	$146.85	$146.80
Purchase #6	$57.71	6.190%	$61.2822	$61.28	$61.30	$61.30
Purchase #7	$80.94	11.569%	$90.3039	$90.30	$90.30	$90.30
7 purchase totals =	$765.97		$829.8853	$829.88	$829.95	$829.80