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	$66.50	11.167%	$73.9261	$73.93	$73.95	$73.90
Purchase #2	$202.82	12.814%	$228.8094	$228.81	$228.80	$228.80
Purchase #3	$110.38	10.461%	$121.9269	$121.93	$121.95	$121.90
Purchase #4	$177.51	10.560%	$196.2551	$196.26	$196.25	$196.30
Purchase #5	$22.93	8.463%	$24.8706	$24.87	$24.85	$24.90
Purchase #6	$41.83	9.720%	$45.8959	$45.90	$45.90	$45.90
Purchase #7	$37.80	8.224%	$40.9087	$40.91	$40.90	$40.90
7 purchase totals =	$659.77		$732.5927	$732.61	$732.60	$732.60