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	$18.32	12.239%	$20.5622	$20.56	$20.55	$20.60
Purchase #2	$149.85	3.167%	$154.5957	$154.60	$154.60	$154.60
Purchase #3	$233.35	3.543%	$241.6176	$241.62	$241.60	$241.60
Purchase #4	$58.83	9.345%	$64.3277	$64.33	$64.35	$64.30
Purchase #5	$249.88	5.510%	$263.6484	$263.65	$263.65	$263.60
Purchase #6	$234.52	10.599%	$259.3768	$259.38	$259.40	$259.40
Purchase #7	$31.41	12.467%	$35.3259	$35.33	$35.35	$35.30
7 purchase totals =	$976.16		$1,039.4543	$1,039.47	$1,039.50	$1,039.40