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	$101.69	6.564%	$108.3649	$108.36	$108.35	$108.40
Purchase #2	$215.70	3.625%	$223.5191	$223.52	$223.50	$223.50
Purchase #3	$175.37	5.761%	$185.4731	$185.47	$185.45	$185.50
Purchase #4	$193.51	10.158%	$213.1667	$213.17	$213.15	$213.20
Purchase #5	$84.79	7.409%	$91.0721	$91.07	$91.05	$91.10
Purchase #6	$87.33	3.113%	$90.0486	$90.05	$90.05	$90.00
Purchase #7	$118.60	10.299%	$130.8146	$130.81	$130.80	$130.80
7 purchase totals =	$976.99		$1,042.4591	$1,042.45	$1,042.35	$1,042.50