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	$122.84	11.595%	$137.0833	$137.08	$137.10	$137.10
Purchase #2	$135.59	6.567%	$144.4942	$144.49	$144.50	$144.50
Purchase #3	$231.72	10.553%	$256.1734	$256.17	$256.15	$256.20
Purchase #4	$83.81	6.191%	$88.9987	$89.00	$89.00	$89.00
Purchase #5	$28.41	11.240%	$31.6033	$31.60	$31.60	$31.60
Purchase #6	$165.96	12.756%	$187.1299	$187.13	$187.15	$187.10
Purchase #7	$145.56	12.549%	$163.8263	$163.83	$163.85	$163.80
7 purchase totals =	$913.89		$1,009.3091	$1,009.30	$1,009.35	$1,009.30