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	$34.57	11.628%	$38.5898	$38.59	$38.60	$38.60
Purchase #2	$25.35	10.698%	$28.0619	$28.06	$28.05	$28.10
Purchase #3	$72.38	11.274%	$80.5401	$80.54	$80.55	$80.50
Purchase #4	$221.40	4.680%	$231.7615	$231.76	$231.75	$231.80
Purchase #5	$138.57	3.801%	$143.837	$143.84	$143.85	$143.80
Purchase #6	$233.69	5.322%	$246.127	$246.13	$246.15	$246.10
Purchase #7	$83.26	10.821%	$92.2696	$92.27	$92.25	$92.30
7 purchase totals =	$809.22		$861.1869	$861.19	$861.20	$861.20