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	$6.89	5.754%	$7.2865	$7.29	$7.30	$7.30
Purchase #2	$214.69	9.710%	$235.5364	$235.54	$235.55	$235.50
Purchase #3	$64.34	8.272%	$69.6622	$69.66	$69.65	$69.70
Purchase #4	$121.28	9.484%	$132.7822	$132.78	$132.80	$132.80
Purchase #5	$98.80	7.155%	$105.8691	$105.87	$105.85	$105.90
Purchase #6	$81.33	9.863%	$89.3516	$89.35	$89.35	$89.40
Purchase #7	$94.47	9.357%	$103.3096	$103.31	$103.30	$103.30
7 purchase totals =	$681.80		$743.7976	$743.80	$743.80	$743.90