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	$83.57	7.724%	$90.0249	$90.02	$90.00	$90.00
Purchase #2	$83.45	12.835%	$94.1608	$94.16	$94.15	$94.20
Purchase #3	$105.91	12.761%	$119.4252	$119.43	$119.45	$119.40
Purchase #4	$155.54	11.254%	$173.0445	$173.04	$173.05	$173.00
Purchase #5	$82.25	13.713%	$93.5289	$93.53	$93.55	$93.50
Purchase #6	$32.43	9.243%	$35.4275	$35.43	$35.45	$35.40
Purchase #7	$85.62	6.452%	$91.1442	$91.14	$91.15	$91.10
7 purchase totals =	$628.77		$696.7560	$696.75	$696.80	$696.60