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	$104.76	13.736%	$119.1498	$119.15	$119.15	$119.10
Purchase #2	$45.89	11.660%	$51.2408	$51.24	$51.25	$51.20
Purchase #3	$126.84	13.223%	$143.6121	$143.61	$143.60	$143.60
Purchase #4	$132.43	13.704%	$150.5782	$150.58	$150.60	$150.60
Purchase #5	$216.82	11.201%	$241.106	$241.11	$241.10	$241.10
Purchase #6	$26.59	12.854%	$30.0079	$30.01	$30.00	$30.00
Purchase #7	$90.77	8.104%	$98.126	$98.13	$98.15	$98.10
7 purchase totals =	$744.10		$833.8208	$833.83	$833.85	$833.70