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	$116.53	13.618%	$132.3991	$132.40	$132.40	$132.40
Purchase #2	$80.85	9.871%	$88.8307	$88.83	$88.85	$88.80
Purchase #3	$46.96	4.686%	$49.1605	$49.16	$49.15	$49.20
Purchase #4	$95.61	5.538%	$100.9049	$100.90	$100.90	$100.90
Purchase #5	$79.43	11.222%	$88.3436	$88.34	$88.35	$88.30
Purchase #6	$47.49	11.420%	$52.9134	$52.91	$52.90	$52.90
Purchase #7	$46.93	9.778%	$51.5188	$51.52	$51.50	$51.50
7 purchase totals =	$513.80		$564.0710	$564.06	$564.05	$564.00