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	$12.55	9.240%	$13.7096	$13.71	$13.70	$13.70
Purchase #2	$34.75	10.705%	$38.47	$38.47	$38.45	$38.50
Purchase #3	$202.83	6.439%	$215.8902	$215.89	$215.90	$215.90
Purchase #4	$250.89	9.642%	$275.0808	$275.08	$275.10	$275.10
Purchase #5	$154.43	8.668%	$167.816	$167.82	$167.80	$167.80
Purchase #6	$88.73	8.398%	$96.1815	$96.18	$96.20	$96.20
Purchase #7	$50.25	6.302%	$53.4168	$53.42	$53.40	$53.40
7 purchase totals =	$794.43		$860.5649	$860.57	$860.55	$860.60