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	$160.27	4.396%	$167.3155	$167.32	$167.30	$167.30
Purchase #2	$219.66	11.681%	$245.3185	$245.32	$245.30	$245.30
Purchase #3	$71.68	9.244%	$78.3061	$78.31	$78.30	$78.30
Purchase #4	$50.72	11.434%	$56.5193	$56.52	$56.50	$56.50
Purchase #5	$20.49	6.617%	$21.8458	$21.85	$21.85	$21.80
Purchase #6	$154.48	12.666%	$174.0464	$174.05	$174.05	$174.00
Purchase #7	$117.93	3.762%	$122.3665	$122.37	$122.35	$122.40
7 purchase totals =	$795.23		$865.7181	$865.74	$865.65	$865.60