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	$89.44	11.855%	$100.0431	$100.04	$100.05	$100.00
Purchase #2	$81.32	4.804%	$85.2266	$85.23	$85.25	$85.20
Purchase #3	$58.40	4.599%	$61.0858	$61.09	$61.10	$61.10
Purchase #4	$94.41	13.693%	$107.3376	$107.34	$107.35	$107.30
Purchase #5	$84.81	12.114%	$95.0839	$95.08	$95.10	$95.10
Purchase #6	$19.34	3.648%	$20.0455	$20.05	$20.05	$20.00
Purchase #7	$103.92	5.615%	$109.7551	$109.76	$109.75	$109.80
7 purchase totals =	$531.64		$578.5776	$578.59	$578.65	$578.50