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	$139.42	11.532%	$155.4979	$155.50	$155.50	$155.50
Purchase #2	$226.82	12.605%	$255.4107	$255.41	$255.40	$255.40
Purchase #3	$25.75	5.337%	$27.1243	$27.12	$27.10	$27.10
Purchase #4	$169.49	8.121%	$183.2543	$183.25	$183.25	$183.30
Purchase #5	$224.96	11.304%	$250.3895	$250.39	$250.40	$250.40
Purchase #6	$177.39	11.321%	$197.4723	$197.47	$197.45	$197.50
Purchase #7	$64.67	11.393%	$72.0379	$72.04	$72.05	$72.00
7 purchase totals =	$1,028.50		$1,141.1869	$1,141.18	$1,141.15	$1,141.20