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	$20.49	3.762%	$21.2608	$21.26	$21.25	$21.30
Purchase #2	$214.95	3.803%	$223.1245	$223.12	$223.10	$223.10
Purchase #3	$63.50	9.167%	$69.321	$69.32	$69.30	$69.30
Purchase #4	$90.34	11.341%	$100.5855	$100.59	$100.60	$100.60
Purchase #5	$167.80	7.167%	$179.8262	$179.83	$179.85	$179.80
Purchase #6	$104.53	5.346%	$110.1182	$110.12	$110.10	$110.10
Purchase #7	$166.82	5.831%	$176.5473	$176.55	$176.55	$176.50
7 purchase totals =	$828.43		$880.7835	$880.79	$880.75	$880.70