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	$230.47	11.780%	$257.6194	$257.62	$257.60	$257.60
Purchase #2	$79.69	4.845%	$83.551	$83.55	$83.55	$83.60
Purchase #3	$222.83	10.254%	$245.679	$245.68	$245.70	$245.70
Purchase #4	$236.59	4.778%	$247.8943	$247.89	$247.90	$247.90
Purchase #5	$137.53	10.440%	$151.8881	$151.89	$151.90	$151.90
Purchase #6	$211.31	9.537%	$231.4626	$231.46	$231.45	$231.50
Purchase #7	$127.71	11.651%	$142.5895	$142.59	$142.60	$142.60
7 purchase totals =	$1,246.13		$1,360.6839	$1,360.68	$1,360.70	$1,360.80