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	$160.81	4.186%	$167.5415	$167.54	$167.55	$167.50
Purchase #2	$147.41	4.134%	$153.5039	$153.50	$153.50	$153.50
Purchase #3	$117.38	12.407%	$131.9433	$131.94	$131.95	$131.90
Purchase #4	$240.45	6.816%	$256.8391	$256.84	$256.85	$256.80
Purchase #5	$30.43	5.576%	$32.1268	$32.13	$32.15	$32.10
Purchase #6	$189.41	8.275%	$205.0837	$205.08	$205.10	$205.10
Purchase #7	$244.94	12.145%	$274.688	$274.69	$274.70	$274.70
7 purchase totals =	$1,130.83		$1,221.7263	$1,221.72	$1,221.80	$1,221.60