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	$26.54	4.489%	$27.7314	$27.73	$27.75	$27.70
Purchase #2	$13.53	6.210%	$14.3702	$14.37	$14.35	$14.40
Purchase #3	$30.84	13.744%	$35.0786	$35.08	$35.10	$35.10
Purchase #4	$33.42	13.150%	$37.8147	$37.81	$37.80	$37.80
Purchase #5	$158.83	8.873%	$172.923	$172.92	$172.90	$172.90
Purchase #6	$90.71	4.278%	$94.5906	$94.59	$94.60	$94.60
Purchase #7	$134.83	5.638%	$142.4317	$142.43	$142.45	$142.40
7 purchase totals =	$488.70		$524.9402	$524.93	$524.95	$524.90