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	$20.95	4.610%	$21.9158	$21.92	$21.90	$21.90
Purchase #2	$110.39	13.622%	$125.4273	$125.43	$125.45	$125.40
Purchase #3	$102.86	13.516%	$116.7626	$116.76	$116.75	$116.80
Purchase #4	$149.85	11.477%	$167.0483	$167.05	$167.05	$167.00
Purchase #5	$199.64	4.379%	$208.3822	$208.38	$208.40	$208.40
Purchase #6	$144.69	5.146%	$152.1357	$152.14	$152.15	$152.10
Purchase #7	$95.42	4.338%	$99.5593	$99.56	$99.55	$99.60
7 purchase totals =	$823.80		$891.2312	$891.24	$891.25	$891.20