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	$31.25	13.534%	$35.4794	$35.48	$35.50	$35.50
Purchase #2	$188.29	10.516%	$208.0906	$208.09	$208.10	$208.10
Purchase #3	$108.28	8.526%	$117.512	$117.51	$117.50	$117.50
Purchase #4	$89.80	11.645%	$100.2572	$100.26	$100.25	$100.30
Purchase #5	$62.25	6.103%	$66.0491	$66.05	$66.05	$66.00
Purchase #6	$48.77	11.661%	$54.4571	$54.46	$54.45	$54.50
Purchase #7	$96.45	8.446%	$104.5962	$104.60	$104.60	$104.60
7 purchase totals =	$625.09		$686.4416	$686.45	$686.45	$686.50