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	$242.94	3.385%	$251.1635	$251.16	$251.15	$251.20
Purchase #2	$57.26	3.841%	$59.4594	$59.46	$59.45	$59.50
Purchase #3	$185.26	13.834%	$210.8889	$210.89	$210.90	$210.90
Purchase #4	$30.59	5.393%	$32.2397	$32.24	$32.25	$32.20
Purchase #5	$217.59	4.594%	$227.5861	$227.59	$227.60	$227.60
Purchase #6	$108.42	5.659%	$114.5555	$114.56	$114.55	$114.60
Purchase #7	$214.38	13.419%	$243.1477	$243.15	$243.15	$243.10
7 purchase totals =	$1,056.44		$1,139.0408	$1,139.05	$1,139.05	$1,139.10