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	$234.44	9.116%	$255.8116	$255.81	$255.80	$255.80
Purchase #2	$117.49	9.243%	$128.3496	$128.35	$128.35	$128.30
Purchase #3	$177.81	8.487%	$192.9007	$192.90	$192.90	$192.90
Purchase #4	$218.38	11.652%	$243.8256	$243.83	$243.85	$243.80
Purchase #5	$45.77	10.183%	$50.4308	$50.43	$50.45	$50.40
Purchase #6	$127.39	13.270%	$144.2947	$144.29	$144.30	$144.30
Purchase #7	$190.85	7.703%	$205.5512	$205.55	$205.55	$205.60
7 purchase totals =	$1,112.13		$1,221.1642	$1,221.16	$1,221.20	$1,221.10