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	$100.64	8.871%	$109.5678	$109.57	$109.55	$109.60
Purchase #2	$124.89	11.690%	$139.4896	$139.49	$139.50	$139.50
Purchase #3	$118.84	13.351%	$134.7063	$134.71	$134.70	$134.70
Purchase #4	$240.67	8.284%	$260.6071	$260.61	$260.60	$260.60
Purchase #5	$46.38	10.237%	$51.1279	$51.13	$51.15	$51.10
Purchase #6	$35.75	5.850%	$37.8414	$37.84	$37.85	$37.80
Purchase #7	$228.28	9.556%	$250.0944	$250.09	$250.10	$250.10
7 purchase totals =	$895.45		$983.4345	$983.44	$983.45	$983.40