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	$240.97	6.286%	$256.1174	$256.12	$256.10	$256.10
Purchase #2	$110.65	3.496%	$114.5183	$114.52	$114.50	$114.50
Purchase #3	$247.67	5.745%	$261.8986	$261.90	$261.90	$261.90
Purchase #4	$129.34	13.366%	$146.6276	$146.63	$146.65	$146.60
Purchase #5	$115.51	3.248%	$119.2618	$119.26	$119.25	$119.30
Purchase #6	$85.60	5.589%	$90.3842	$90.38	$90.40	$90.40
Purchase #7	$47.27	9.281%	$51.6571	$51.66	$51.65	$51.70
7 purchase totals =	$977.01		$1,040.4650	$1,040.47	$1,040.45	$1,040.50