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	$30.27	9.296%	$33.0839	$33.08	$33.10	$33.10
Purchase #2	$73.54	10.224%	$81.0587	$81.06	$81.05	$81.10
Purchase #3	$9.71	11.784%	$10.8542	$10.85	$10.85	$10.90
Purchase #4	$146.90	6.868%	$156.9891	$156.99	$157.00	$157.00
Purchase #5	$78.64	6.144%	$83.4716	$83.47	$83.45	$83.50
Purchase #6	$36.59	3.224%	$37.7697	$37.77	$37.75	$37.80
Purchase #7	$93.29	11.365%	$103.8924	$103.89	$103.90	$103.90
7 purchase totals =	$468.94		$507.1196	$507.11	$507.10	$507.30