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	$225.84	5.226%	$237.6424	$237.64	$237.65	$237.60
Purchase #2	$32.81	8.384%	$35.5608	$35.56	$35.55	$35.60
Purchase #3	$17.29	13.316%	$19.5923	$19.59	$19.60	$19.60
Purchase #4	$21.29	13.453%	$24.1541	$24.15	$24.15	$24.20
Purchase #5	$96.89	4.140%	$100.9012	$100.90	$100.90	$100.90
Purchase #6	$59.73	13.564%	$67.8318	$67.83	$67.85	$67.80
Purchase #7	$192.89	5.772%	$204.0236	$204.02	$204.00	$204.00
7 purchase totals =	$646.74		$689.7062	$689.69	$689.70	$689.70