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	$32.40	6.487%	$34.5018	$34.50	$34.50	$34.50
Purchase #2	$72.40	6.228%	$76.9091	$76.91	$76.90	$76.90
Purchase #3	$143.60	5.138%	$150.9782	$150.98	$151.00	$151.00
Purchase #4	$27.25	7.686%	$29.3444	$29.34	$29.35	$29.30
Purchase #5	$175.87	9.417%	$192.4317	$192.43	$192.45	$192.40
Purchase #6	$93.38	10.819%	$103.4828	$103.48	$103.50	$103.50
Purchase #7	$61.87	6.224%	$65.7208	$65.72	$65.70	$65.70
7 purchase totals =	$606.77		$653.3688	$653.36	$653.40	$653.30