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	$37.83	7.127%	$40.5261	$40.53	$40.55	$40.50
Purchase #2	$198.34	13.739%	$225.5899	$225.59	$225.60	$225.60
Purchase #3	$92.82	10.544%	$102.6069	$102.61	$102.60	$102.60
Purchase #4	$76.43	9.211%	$83.47	$83.47	$83.45	$83.50
Purchase #5	$155.74	8.705%	$169.2972	$169.30	$169.30	$169.30
Purchase #6	$120.41	11.654%	$134.4426	$134.44	$134.45	$134.40
Purchase #7	$220.26	4.797%	$230.8259	$230.83	$230.85	$230.80
7 purchase totals =	$901.83		$986.7586	$986.77	$986.80	$986.70