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	$113.66	12.249%	$127.5822	$127.58	$127.60	$127.60
Purchase #2	$120.85	8.825%	$131.515	$131.52	$131.50	$131.50
Purchase #3	$223.69	6.696%	$238.6683	$238.67	$238.65	$238.70
Purchase #4	$59.49	4.442%	$62.1325	$62.13	$62.15	$62.10
Purchase #5	$134.45	6.175%	$142.7523	$142.75	$142.75	$142.80
Purchase #6	$60.71	9.287%	$66.3481	$66.35	$66.35	$66.30
Purchase #7	$58.70	12.755%	$66.1872	$66.19	$66.20	$66.20
7 purchase totals =	$771.55		$835.1856	$835.19	$835.20	$835.20