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	$71.86	9.730%	$78.852	$78.85	$78.85	$78.90
Purchase #2	$60.98	5.261%	$64.1882	$64.19	$64.20	$64.20
Purchase #3	$165.45	5.640%	$174.7814	$174.78	$174.80	$174.80
Purchase #4	$142.72	5.668%	$150.8094	$150.81	$150.80	$150.80
Purchase #5	$145.63	10.617%	$161.0915	$161.09	$161.10	$161.10
Purchase #6	$10.36	6.235%	$11.0059	$11.01	$11.00	$11.00
Purchase #7	$125.51	4.476%	$131.1278	$131.13	$131.15	$131.10
7 purchase totals =	$722.51		$771.8562	$771.86	$771.90	$771.90