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	$116.34	13.275%	$131.7841	$131.78	$131.80	$131.80
Purchase #2	$105.43	5.491%	$111.2192	$111.22	$111.20	$111.20
Purchase #3	$23.61	3.609%	$24.4621	$24.46	$24.45	$24.50
Purchase #4	$250.68	8.416%	$271.7772	$271.78	$271.80	$271.80
Purchase #5	$214.94	6.542%	$229.0014	$229.00	$229.00	$229.00
Purchase #6	$114.86	7.188%	$123.1161	$123.12	$123.10	$123.10
Purchase #7	$117.98	6.591%	$125.7561	$125.76	$125.75	$125.80
7 purchase totals =	$943.84		$1,017.1162	$1,017.12	$1,017.10	$1,017.20