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	$9.52	8.324%	$10.3124	$10.31	$10.30	$10.30
Purchase #2	$69.49	13.310%	$78.7391	$78.74	$78.75	$78.70
Purchase #3	$187.89	13.641%	$213.5201	$213.52	$213.50	$213.50
Purchase #4	$139.48	6.215%	$148.1487	$148.15	$148.15	$148.10
Purchase #5	$23.59	8.532%	$25.6027	$25.60	$25.60	$25.60
Purchase #6	$78.31	11.700%	$87.4723	$87.47	$87.45	$87.50
Purchase #7	$68.75	5.769%	$72.7162	$72.72	$72.70	$72.70
7 purchase totals =	$577.03		$636.5115	$636.51	$636.45	$636.40