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	$138.84	3.634%	$143.8854	$143.89	$143.90	$143.90
Purchase #2	$205.85	13.639%	$233.9259	$233.93	$233.95	$233.90
Purchase #3	$233.34	12.459%	$262.4118	$262.41	$262.40	$262.40
Purchase #4	$231.44	3.166%	$238.7674	$238.77	$238.75	$238.80
Purchase #5	$17.25	9.485%	$18.8862	$18.89	$18.90	$18.90
Purchase #6	$245.54	12.353%	$275.8716	$275.87	$275.85	$275.90
Purchase #7	$249.89	4.595%	$261.3724	$261.37	$261.35	$261.40
7 purchase totals =	$1,322.15		$1,435.1207	$1,435.13	$1,435.10	$1,435.20