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	$91.58	9.768%	$100.5255	$100.53	$100.55	$100.50
Purchase #2	$59.82	13.106%	$67.66	$67.66	$67.65	$67.70
Purchase #3	$160.98	9.635%	$176.4904	$176.49	$176.50	$176.50
Purchase #4	$135.35	7.846%	$145.9696	$145.97	$145.95	$146.00
Purchase #5	$156.93	7.486%	$168.6778	$168.68	$168.70	$168.70
Purchase #6	$177.82	10.376%	$196.2706	$196.27	$196.25	$196.30
Purchase #7	$39.70	4.518%	$41.4936	$41.49	$41.50	$41.50
7 purchase totals =	$822.18		$897.0875	$897.09	$897.10	$897.20