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	$137.45	8.328%	$148.8968	$148.90	$148.90	$148.90
Purchase #2	$27.40	12.693%	$30.8779	$30.88	$30.90	$30.90
Purchase #3	$125.85	4.463%	$131.4667	$131.47	$131.45	$131.50
Purchase #4	$95.34	8.778%	$103.7089	$103.71	$103.70	$103.70
Purchase #5	$129.78	6.343%	$138.0119	$138.01	$138.00	$138.00
Purchase #6	$62.57	13.590%	$71.0733	$71.07	$71.05	$71.10
Purchase #7	$89.90	5.427%	$94.7789	$94.78	$94.80	$94.80
7 purchase totals =	$668.29		$718.8144	$718.82	$718.80	$718.90