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	$25.37	9.804%	$27.8573	$27.86	$27.85	$27.90
Purchase #2	$37.48	3.734%	$38.8795	$38.88	$38.90	$38.90
Purchase #3	$49.43	12.473%	$55.5954	$55.60	$55.60	$55.60
Purchase #4	$162.40	5.197%	$170.8399	$170.84	$170.85	$170.80
Purchase #5	$51.97	7.854%	$56.0517	$56.05	$56.05	$56.10
Purchase #6	$119.27	8.131%	$128.9678	$128.97	$128.95	$129.00
Purchase #7	$6.46	12.209%	$7.2487	$7.25	$7.25	$7.20
7 purchase totals =	$452.38		$485.4403	$485.45	$485.45	$485.50