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	$87.78	3.673%	$91.0042	$91.00	$91.00	$91.00
Purchase #2	$82.60	8.532%	$89.6474	$89.65	$89.65	$89.60
Purchase #3	$140.95	12.143%	$158.0656	$158.07	$158.05	$158.10
Purchase #4	$49.25	12.865%	$55.586	$55.59	$55.60	$55.60
Purchase #5	$69.87	3.316%	$72.1869	$72.19	$72.20	$72.20
Purchase #6	$245.69	4.664%	$257.149	$257.15	$257.15	$257.10
Purchase #7	$92.81	6.664%	$98.9949	$98.99	$99.00	$99.00
7 purchase totals =	$768.95		$822.6340	$822.64	$822.65	$822.60