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	$28.53	3.874%	$29.6353	$29.64	$29.65	$29.60
Purchase #2	$93.43	11.456%	$104.1333	$104.13	$104.15	$104.10
Purchase #3	$89.26	7.302%	$95.7778	$95.78	$95.80	$95.80
Purchase #4	$57.74	13.240%	$65.3848	$65.38	$65.40	$65.40
Purchase #5	$147.49	11.365%	$164.2522	$164.25	$164.25	$164.30
Purchase #6	$69.42	4.563%	$72.5876	$72.59	$72.60	$72.60
Purchase #7	$57.95	8.818%	$63.06	$63.06	$63.05	$63.10
7 purchase totals =	$543.82		$594.8310	$594.83	$594.90	$594.90