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	$69.48	11.682%	$77.5967	$77.60	$77.60	$77.60
Purchase #2	$78.47	8.747%	$85.3338	$85.33	$85.35	$85.30
Purchase #3	$79.81	7.248%	$85.5946	$85.59	$85.60	$85.60
Purchase #4	$157.36	4.602%	$164.6017	$164.60	$164.60	$164.60
Purchase #5	$117.25	8.471%	$127.1822	$127.18	$127.20	$127.20
Purchase #6	$103.39	6.553%	$110.1651	$110.17	$110.15	$110.20
Purchase #7	$86.67	3.143%	$89.394	$89.39	$89.40	$89.40
7 purchase totals =	$692.43		$739.8681	$739.86	$739.90	$739.90