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	$52.60	13.704%	$59.8083	$59.81	$59.80	$59.80
Purchase #2	$47.90	11.148%	$53.2399	$53.24	$53.25	$53.20
Purchase #3	$44.93	3.316%	$46.4199	$46.42	$46.40	$46.40
Purchase #4	$83.29	9.192%	$90.946	$90.95	$90.95	$90.90
Purchase #5	$5.50	6.468%	$5.8557	$5.86	$5.85	$5.90
Purchase #6	$74.85	10.779%	$82.9181	$82.92	$82.90	$82.90
Purchase #7	$80.91	4.315%	$84.4013	$84.40	$84.40	$84.40
7 purchase totals =	$389.98		$423.5892	$423.60	$423.55	$423.50