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	$226.40	13.701%	$257.4191	$257.42	$257.40	$257.40
Purchase #2	$186.47	10.455%	$205.9654	$205.97	$205.95	$206.00
Purchase #3	$216.77	4.462%	$226.4423	$226.44	$226.45	$226.40
Purchase #4	$10.59	12.295%	$11.892	$11.89	$11.90	$11.90
Purchase #5	$205.59	8.578%	$223.2255	$223.23	$223.25	$223.20
Purchase #6	$145.68	13.607%	$165.5027	$165.50	$165.50	$165.50
Purchase #7	$90.43	9.326%	$98.8635	$98.86	$98.85	$98.90
7 purchase totals =	$1,081.93		$1,189.3105	$1,189.31	$1,189.30	$1,189.30