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	$63.82	3.821%	$66.2586	$66.26	$66.25	$66.30
Purchase #2	$105.44	5.592%	$111.3362	$111.34	$111.35	$111.30
Purchase #3	$98.56	7.517%	$105.9688	$105.97	$105.95	$106.00
Purchase #4	$116.89	9.134%	$127.5667	$127.57	$127.55	$127.60
Purchase #5	$97.97	7.326%	$105.1473	$105.15	$105.15	$105.10
Purchase #6	$56.26	11.811%	$62.9049	$62.90	$62.90	$62.90
Purchase #7	$7.64	12.239%	$8.5751	$8.58	$8.60	$8.60
7 purchase totals =	$546.58		$587.7576	$587.77	$587.75	$587.80