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	$45.51	10.623%	$50.3445	$50.34	$50.35	$50.30
Purchase #2	$180.61	4.724%	$189.142	$189.14	$189.15	$189.10
Purchase #3	$182.54	13.169%	$206.5787	$206.58	$206.60	$206.60
Purchase #4	$11.96	5.264%	$12.5896	$12.59	$12.60	$12.60
Purchase #5	$89.63	10.615%	$99.1442	$99.14	$99.15	$99.10
Purchase #6	$191.44	3.496%	$198.1327	$198.13	$198.15	$198.10
Purchase #7	$91.71	13.597%	$104.1798	$104.18	$104.20	$104.20
7 purchase totals =	$793.40		$860.1115	$860.10	$860.20	$860.00