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	$222.70	7.217%	$238.7723	$238.77	$238.75	$238.80
Purchase #2	$137.99	7.510%	$148.353	$148.35	$148.35	$148.40
Purchase #3	$83.80	8.569%	$90.9808	$90.98	$91.00	$91.00
Purchase #4	$34.34	4.829%	$35.9983	$36.00	$36.00	$36.00
Purchase #5	$126.36	12.737%	$142.4545	$142.45	$142.45	$142.50
Purchase #6	$119.92	11.396%	$133.5861	$133.59	$133.60	$133.60
Purchase #7	$87.82	13.392%	$99.5809	$99.58	$99.60	$99.60
7 purchase totals =	$812.93		$889.7259	$889.72	$889.75	$889.90