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	$36.82	9.719%	$40.3985	$40.40	$40.40	$40.40
Purchase #2	$175.89	11.818%	$196.6767	$196.68	$196.70	$196.70
Purchase #3	$51.77	12.262%	$58.118	$58.12	$58.10	$58.10
Purchase #4	$45.37	12.366%	$50.9805	$50.98	$51.00	$51.00
Purchase #5	$215.89	6.591%	$230.1193	$230.12	$230.10	$230.10
Purchase #6	$220.43	13.177%	$249.4761	$249.48	$249.50	$249.50
Purchase #7	$232.79	5.599%	$245.8239	$245.82	$245.80	$245.80
7 purchase totals =	$978.96		$1,071.5930	$1,071.60	$1,071.60	$1,071.60