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	$59.83	12.704%	$67.4308	$67.43	$67.45	$67.40
Purchase #2	$82.34	8.676%	$89.4838	$89.48	$89.50	$89.50
Purchase #3	$63.95	8.568%	$69.4292	$69.43	$69.45	$69.40
Purchase #4	$177.54	7.668%	$191.1538	$191.15	$191.15	$191.20
Purchase #5	$48.61	13.344%	$55.0965	$55.10	$55.10	$55.10
Purchase #6	$78.74	13.788%	$89.5967	$89.60	$89.60	$89.60
Purchase #7	$230.74	12.513%	$259.6125	$259.61	$259.60	$259.60
7 purchase totals =	$741.75		$821.8033	$821.80	$821.85	$821.80