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	$245.57	13.410%	$278.5009	$278.50	$278.50	$278.50
Purchase #2	$137.55	13.368%	$155.9377	$155.94	$155.95	$155.90
Purchase #3	$88.73	12.640%	$99.9455	$99.95	$99.95	$99.90
Purchase #4	$125.28	9.118%	$136.703	$136.70	$136.70	$136.70
Purchase #5	$35.75	13.286%	$40.4997	$40.50	$40.50	$40.50
Purchase #6	$92.36	10.398%	$101.9636	$101.96	$101.95	$102.00
Purchase #7	$208.61	10.705%	$230.9417	$230.94	$230.95	$230.90
7 purchase totals =	$933.85		$1,044.4921	$1,044.49	$1,044.50	$1,044.40