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	$99.84	13.725%	$113.543	$113.54	$113.55	$113.50
Purchase #2	$243.49	10.326%	$268.6328	$268.63	$268.65	$268.60
Purchase #3	$65.71	13.731%	$74.7326	$74.73	$74.75	$74.70
Purchase #4	$194.72	5.737%	$205.8911	$205.89	$205.90	$205.90
Purchase #5	$29.27	13.381%	$33.1866	$33.19	$33.20	$33.20
Purchase #6	$84.65	5.779%	$89.5419	$89.54	$89.55	$89.50
Purchase #7	$190.55	7.853%	$205.5139	$205.51	$205.50	$205.50
7 purchase totals =	$908.23		$991.0419	$991.03	$991.10	$990.90