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	$226.68	13.381%	$257.0121	$257.01	$257.00	$257.00
Purchase #2	$10.73	7.510%	$11.5358	$11.54	$11.55	$11.50
Purchase #3	$127.73	10.580%	$141.2438	$141.24	$141.25	$141.20
Purchase #4	$33.95	7.151%	$36.3778	$36.38	$36.40	$36.40
Purchase #5	$76.33	9.378%	$83.4882	$83.49	$83.50	$83.50
Purchase #6	$183.79	13.494%	$208.5906	$208.59	$208.60	$208.60
Purchase #7	$18.89	6.152%	$20.0521	$20.05	$20.05	$20.10
7 purchase totals =	$678.10		$758.3004	$758.30	$758.35	$758.30