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	$231.85	5.575%	$244.7756	$244.78	$244.80	$244.80
Purchase #2	$241.53	10.429%	$266.7192	$266.72	$266.70	$266.70
Purchase #3	$60.39	3.209%	$62.3279	$62.33	$62.35	$62.30
Purchase #4	$33.31	9.417%	$36.4468	$36.45	$36.45	$36.40
Purchase #5	$75.31	3.414%	$77.8811	$77.88	$77.90	$77.90
Purchase #6	$170.64	9.856%	$187.4583	$187.46	$187.45	$187.50
Purchase #7	$7.83	6.553%	$8.3431	$8.34	$8.35	$8.30
7 purchase totals =	$820.86		$883.9520	$883.96	$884.00	$883.90