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	$19.35	6.316%	$20.5721	$20.57	$20.55	$20.60
Purchase #2	$213.75	11.147%	$237.5767	$237.58	$237.60	$237.60
Purchase #3	$201.27	10.707%	$222.82	$222.82	$222.80	$222.80
Purchase #4	$35.48	11.314%	$39.4942	$39.49	$39.50	$39.50
Purchase #5	$120.35	8.823%	$130.9685	$130.97	$130.95	$131.00
Purchase #6	$250.45	6.668%	$267.15	$267.15	$267.15	$267.20
Purchase #7	$203.73	11.544%	$227.2486	$227.25	$227.25	$227.20
7 purchase totals =	$1,044.38		$1,145.8301	$1,145.83	$1,145.80	$1,145.90