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	$150.56	3.274%	$155.4893	$155.49	$155.50	$155.50
Purchase #2	$142.34	13.448%	$161.4819	$161.48	$161.50	$161.50
Purchase #3	$132.34	8.843%	$144.0428	$144.04	$144.05	$144.00
Purchase #4	$33.92	8.314%	$36.7401	$36.74	$36.75	$36.70
Purchase #5	$127.83	7.300%	$137.1616	$137.16	$137.15	$137.20
Purchase #6	$151.66	5.593%	$160.1423	$160.14	$160.15	$160.10
Purchase #7	$38.42	5.176%	$40.4086	$40.41	$40.40	$40.40
7 purchase totals =	$777.07		$835.4666	$835.46	$835.50	$835.40