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	$39.78	4.509%	$41.5737	$41.57	$41.55	$41.60
Purchase #2	$159.54	12.780%	$179.9292	$179.93	$179.95	$179.90
Purchase #3	$160.66	4.123%	$167.284	$167.28	$167.30	$167.30
Purchase #4	$116.70	13.235%	$132.1452	$132.15	$132.15	$132.10
Purchase #5	$58.54	4.572%	$61.2164	$61.22	$61.20	$61.20
Purchase #6	$175.87	10.599%	$194.5105	$194.51	$194.50	$194.50
Purchase #7	$69.85	3.588%	$72.3562	$72.36	$72.35	$72.40
7 purchase totals =	$780.94		$849.0152	$849.02	$849.00	$849.00