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	$144.54	13.585%	$164.1758	$164.18	$164.20	$164.20
Purchase #2	$117.54	10.292%	$129.6372	$129.64	$129.65	$129.60
Purchase #3	$160.27	9.293%	$175.1639	$175.16	$175.15	$175.20
Purchase #4	$27.25	7.484%	$29.2894	$29.29	$29.30	$29.30
Purchase #5	$89.43	11.274%	$99.5123	$99.51	$99.50	$99.50
Purchase #6	$153.31	3.656%	$158.915	$158.92	$158.90	$158.90
Purchase #7	$29.37	6.604%	$31.3096	$31.31	$31.30	$31.30
7 purchase totals =	$721.71		$788.0032	$788.01	$788.00	$788.00