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	$78.31	5.383%	$82.5254	$82.53	$82.55	$82.50
Purchase #2	$59.52	10.622%	$65.8422	$65.84	$65.85	$65.80
Purchase #3	$119.83	11.831%	$134.0071	$134.01	$134.00	$134.00
Purchase #4	$68.38	8.514%	$74.2019	$74.20	$74.20	$74.20
Purchase #5	$145.90	11.423%	$162.5662	$162.57	$162.55	$162.60
Purchase #6	$33.34	6.592%	$35.5378	$35.54	$35.55	$35.50
Purchase #7	$38.80	10.521%	$42.8821	$42.88	$42.90	$42.90
7 purchase totals =	$544.08		$597.5627	$597.57	$597.60	$597.50