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	$10.86	11.868%	$12.1489	$12.15	$12.15	$12.10
Purchase #2	$147.44	11.398%	$164.2452	$164.25	$164.25	$164.20
Purchase #3	$10.38	6.597%	$11.0648	$11.06	$11.05	$11.10
Purchase #4	$218.65	11.351%	$243.469	$243.47	$243.45	$243.50
Purchase #5	$139.82	7.667%	$150.54	$150.54	$150.55	$150.50
Purchase #6	$26.69	5.381%	$28.1262	$28.13	$28.15	$28.10
Purchase #7	$221.69	4.440%	$231.533	$231.53	$231.55	$231.50
7 purchase totals =	$775.53		$841.1271	$841.13	$841.15	$841.00