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	$99.87	10.688%	$110.5441	$110.54	$110.55	$110.50
Purchase #2	$249.89	9.110%	$272.655	$272.66	$272.65	$272.70
Purchase #3	$238.92	10.456%	$263.9015	$263.90	$263.90	$263.90
Purchase #4	$175.38	12.229%	$196.8272	$196.83	$196.85	$196.80
Purchase #5	$84.65	12.846%	$95.5241	$95.52	$95.50	$95.50
Purchase #6	$137.87	11.462%	$153.6727	$153.67	$153.65	$153.70
Purchase #7	$132.34	10.543%	$146.2926	$146.29	$146.30	$146.30
7 purchase totals =	$1,118.92		$1,239.4172	$1,239.41	$1,239.40	$1,239.40