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	$13.85	11.374%	$15.4253	$15.43	$15.45	$15.40
Purchase #2	$118.58	5.756%	$125.4055	$125.41	$125.40	$125.40
Purchase #3	$7.88	5.811%	$8.3379	$8.34	$8.35	$8.30
Purchase #4	$132.53	8.220%	$143.424	$143.42	$143.40	$143.40
Purchase #5	$92.32	12.786%	$104.124	$104.12	$104.10	$104.10
Purchase #6	$11.72	4.348%	$12.2296	$12.23	$12.25	$12.20
Purchase #7	$118.43	4.572%	$123.8446	$123.84	$123.85	$123.80
7 purchase totals =	$495.31		$532.7909	$532.79	$532.80	$532.60