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	$8.91	12.461%	$10.0203	$10.02	$10.00	$10.00
Purchase #2	$166.40	11.116%	$184.897	$184.90	$184.90	$184.90
Purchase #3	$90.85	12.491%	$102.1981	$102.20	$102.20	$102.20
Purchase #4	$160.32	6.343%	$170.4891	$170.49	$170.50	$170.50
Purchase #5	$166.39	13.300%	$188.5199	$188.52	$188.50	$188.50
Purchase #6	$209.81	8.466%	$227.5725	$227.57	$227.55	$227.60
Purchase #7	$105.59	3.721%	$109.519	$109.52	$109.50	$109.50
7 purchase totals =	$908.27		$993.2159	$993.22	$993.15	$993.20