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	$120.67	8.814%	$131.3059	$131.31	$131.30	$131.30
Purchase #2	$109.92	4.473%	$114.8367	$114.84	$114.85	$114.80
Purchase #3	$85.57	7.620%	$92.0904	$92.09	$92.10	$92.10
Purchase #4	$58.59	10.558%	$64.7759	$64.78	$64.80	$64.80
Purchase #5	$182.44	12.622%	$205.4676	$205.47	$205.45	$205.50
Purchase #6	$62.57	6.295%	$66.5088	$66.51	$66.50	$66.50
Purchase #7	$145.43	13.623%	$165.2419	$165.24	$165.25	$165.20
7 purchase totals =	$765.19		$840.2272	$840.24	$840.25	$840.20