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	$217.71	12.642%	$245.2329	$245.23	$245.25	$245.20
Purchase #2	$102.46	12.704%	$115.4765	$115.48	$115.50	$115.50
Purchase #3	$168.73	12.788%	$190.3072	$190.31	$190.30	$190.30
Purchase #4	$227.49	12.708%	$256.3994	$256.40	$256.40	$256.40
Purchase #5	$101.86	9.681%	$111.7211	$111.72	$111.70	$111.70
Purchase #6	$19.94	9.819%	$21.8979	$21.90	$21.90	$21.90
Purchase #7	$95.40	6.823%	$101.9091	$101.91	$101.90	$101.90
7 purchase totals =	$933.59		$1,042.9441	$1,042.95	$1,042.95	$1,042.90