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	$131.96	3.322%	$136.3437	$136.34	$136.35	$136.30
Purchase #2	$20.55	5.670%	$21.7152	$21.72	$21.70	$21.70
Purchase #3	$160.93	11.124%	$178.8319	$178.83	$178.85	$178.80
Purchase #4	$71.43	10.213%	$78.7251	$78.73	$78.75	$78.70
Purchase #5	$6.86	5.481%	$7.236	$7.24	$7.25	$7.20
Purchase #6	$242.38	8.127%	$262.0782	$262.08	$262.10	$262.10
Purchase #7	$117.48	9.302%	$128.408	$128.41	$128.40	$128.40
7 purchase totals =	$751.59		$813.3381	$813.35	$813.40	$813.20