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	$62.35	13.117%	$70.5284	$70.53	$70.55	$70.50
Purchase #2	$141.36	12.424%	$158.9226	$158.92	$158.90	$158.90
Purchase #3	$94.37	9.677%	$103.5022	$103.50	$103.50	$103.50
Purchase #4	$73.98	10.593%	$81.8167	$81.82	$81.80	$81.80
Purchase #5	$241.91	5.790%	$255.9166	$255.92	$255.90	$255.90
Purchase #6	$58.82	6.641%	$62.7262	$62.73	$62.75	$62.70
Purchase #7	$204.86	4.117%	$213.2941	$213.29	$213.30	$213.30
7 purchase totals =	$877.65		$946.7068	$946.71	$946.70	$946.60