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	$21.75	9.870%	$23.8967	$23.90	$23.90	$23.90
Purchase #2	$166.46	3.746%	$172.6956	$172.70	$172.70	$172.70
Purchase #3	$128.26	12.822%	$144.7055	$144.71	$144.70	$144.70
Purchase #4	$223.41	13.484%	$253.5346	$253.53	$253.55	$253.50
Purchase #5	$219.84	6.353%	$233.8064	$233.81	$233.80	$233.80
Purchase #6	$164.38	7.714%	$177.0603	$177.06	$177.05	$177.10
Purchase #7	$167.67	10.660%	$185.5436	$185.54	$185.55	$185.50
7 purchase totals =	$1,091.77		$1,191.2427	$1,191.25	$1,191.25	$1,191.20