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	$86.47	3.545%	$89.5354	$89.54	$89.55	$89.50
Purchase #2	$89.73	10.683%	$99.3159	$99.32	$99.30	$99.30
Purchase #3	$5.42	3.219%	$5.5945	$5.59	$5.60	$5.60
Purchase #4	$208.48	11.796%	$233.0723	$233.07	$233.05	$233.10
Purchase #5	$163.46	3.789%	$169.6535	$169.65	$169.65	$169.70
Purchase #6	$8.90	5.461%	$9.386	$9.39	$9.40	$9.40
Purchase #7	$9.39	13.721%	$10.6784	$10.68	$10.70	$10.70
7 purchase totals =	$571.85		$617.2360	$617.24	$617.25	$617.30