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	$107.47	3.835%	$111.5915	$111.59	$111.60	$111.60
Purchase #2	$150.32	11.703%	$167.9119	$167.91	$167.90	$167.90
Purchase #3	$242.29	5.395%	$255.3615	$255.36	$255.35	$255.40
Purchase #4	$192.77	5.552%	$203.4726	$203.47	$203.45	$203.50
Purchase #5	$235.51	13.362%	$266.9788	$266.98	$267.00	$267.00
Purchase #6	$207.25	6.266%	$220.2363	$220.24	$220.25	$220.20
Purchase #7	$42.56	6.580%	$45.3604	$45.36	$45.35	$45.40
7 purchase totals =	$1,178.17		$1,270.9130	$1,270.91	$1,270.90	$1,271.00