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	$31.44	8.811%	$34.2102	$34.21	$34.20	$34.20
Purchase #2	$18.72	11.575%	$20.8868	$20.89	$20.90	$20.90
Purchase #3	$162.47	6.402%	$172.8713	$172.87	$172.85	$172.90
Purchase #4	$242.27	5.399%	$255.3502	$255.35	$255.35	$255.40
Purchase #5	$13.27	4.292%	$13.8395	$13.84	$13.85	$13.80
Purchase #6	$214.46	8.619%	$232.9443	$232.94	$232.95	$232.90
Purchase #7	$64.92	10.126%	$71.4938	$71.49	$71.50	$71.50
7 purchase totals =	$747.55		$801.5961	$801.59	$801.60	$801.60