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	$66.60	6.434%	$70.885	$70.89	$70.90	$70.90
Purchase #2	$79.93	3.754%	$82.9306	$82.93	$82.95	$82.90
Purchase #3	$57.25	13.265%	$64.8442	$64.84	$64.85	$64.80
Purchase #4	$155.98	7.828%	$168.1901	$168.19	$168.20	$168.20
Purchase #5	$188.30	12.238%	$211.3442	$211.34	$211.35	$211.30
Purchase #6	$134.84	12.390%	$151.5467	$151.55	$151.55	$151.50
Purchase #7	$52.47	5.203%	$55.2	$55.20	$55.20	$55.20
7 purchase totals =	$735.37		$804.9408	$804.94	$805.00	$804.80