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	$128.26	13.539%	$145.6251	$145.63	$145.65	$145.60
Purchase #2	$208.47	9.619%	$228.5227	$228.52	$228.50	$228.50
Purchase #3	$134.81	4.782%	$141.2566	$141.26	$141.25	$141.30
Purchase #4	$130.72	10.823%	$144.8678	$144.87	$144.85	$144.90
Purchase #5	$181.80	3.320%	$187.8358	$187.84	$187.85	$187.80
Purchase #6	$31.51	12.706%	$35.5137	$35.51	$35.50	$35.50
Purchase #7	$27.76	7.758%	$29.9136	$29.91	$29.90	$29.90
7 purchase totals =	$843.33		$913.5353	$913.54	$913.50	$913.50