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	$23.70	5.360%	$24.9703	$24.97	$24.95	$25.00
Purchase #2	$141.65	6.443%	$150.7765	$150.78	$150.80	$150.80
Purchase #3	$88.94	6.461%	$94.6864	$94.69	$94.70	$94.70
Purchase #4	$39.60	11.725%	$44.2431	$44.24	$44.25	$44.20
Purchase #5	$51.89	12.328%	$58.287	$58.29	$58.30	$58.30
Purchase #6	$101.32	9.674%	$111.1217	$111.12	$111.10	$111.10
Purchase #7	$141.91	12.371%	$159.4657	$159.47	$159.45	$159.50
7 purchase totals =	$589.01		$643.5507	$643.56	$643.55	$643.60