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	$212.88	5.644%	$224.8949	$224.89	$224.90	$224.90
Purchase #2	$187.85	9.623%	$205.9268	$205.93	$205.95	$205.90
Purchase #3	$229.40	4.319%	$239.3078	$239.31	$239.30	$239.30
Purchase #4	$132.71	7.320%	$142.4244	$142.42	$142.40	$142.40
Purchase #5	$11.82	4.382%	$12.338	$12.34	$12.35	$12.30
Purchase #6	$25.81	6.348%	$27.4484	$27.45	$27.45	$27.40
Purchase #7	$152.82	10.184%	$168.3832	$168.38	$168.40	$168.40
7 purchase totals =	$953.29		$1,020.7235	$1,020.72	$1,020.75	$1,020.60