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	$83.54	7.669%	$89.9467	$89.95	$89.95	$89.90
Purchase #2	$228.32	4.483%	$238.5556	$238.56	$238.55	$238.60
Purchase #3	$235.94	5.406%	$248.6949	$248.69	$248.70	$248.70
Purchase #4	$119.31	6.124%	$126.6165	$126.62	$126.60	$126.60
Purchase #5	$35.83	8.348%	$38.8211	$38.82	$38.80	$38.80
Purchase #6	$109.37	7.718%	$117.8112	$117.81	$117.80	$117.80
Purchase #7	$137.31	4.518%	$143.5137	$143.51	$143.50	$143.50
7 purchase totals =	$949.62		$1,003.9597	$1,003.96	$1,003.90	$1,003.90