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	$38.31	5.793%	$40.5293	$40.53	$40.55	$40.50
Purchase #2	$109.44	12.839%	$123.491	$123.49	$123.50	$123.50
Purchase #3	$99.37	4.543%	$103.8844	$103.88	$103.90	$103.90
Purchase #4	$41.88	10.175%	$46.1413	$46.14	$46.15	$46.10
Purchase #5	$36.99	12.718%	$41.6944	$41.69	$41.70	$41.70
Purchase #6	$33.98	9.667%	$37.2648	$37.26	$37.25	$37.30
Purchase #7	$168.38	4.466%	$175.8999	$175.90	$175.90	$175.90
7 purchase totals =	$528.35		$568.9051	$568.89	$568.95	$568.90