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	$115.91	13.776%	$131.8778	$131.88	$131.90	$131.90
Purchase #2	$153.81	9.405%	$168.2758	$168.28	$168.30	$168.30
Purchase #3	$96.41	12.174%	$108.147	$108.15	$108.15	$108.10
Purchase #4	$134.41	10.604%	$148.6628	$148.66	$148.65	$148.70
Purchase #5	$36.29	11.620%	$40.5069	$40.51	$40.50	$40.50
Purchase #6	$155.54	8.256%	$168.3814	$168.38	$168.40	$168.40
Purchase #7	$26.43	10.215%	$29.1298	$29.13	$29.15	$29.10
7 purchase totals =	$718.80		$794.9815	$794.99	$795.05	$795.00