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	$78.70	13.471%	$89.3017	$89.30	$89.30	$89.30
Purchase #2	$195.93	4.650%	$205.0407	$205.04	$205.05	$205.00
Purchase #3	$166.37	11.297%	$185.1648	$185.16	$185.15	$185.20
Purchase #4	$51.65	9.179%	$56.391	$56.39	$56.40	$56.40
Purchase #5	$205.57	3.609%	$212.989	$212.99	$213.00	$213.00
Purchase #6	$22.51	13.394%	$25.525	$25.53	$25.55	$25.50
Purchase #7	$93.39	10.769%	$103.4472	$103.45	$103.45	$103.40
7 purchase totals =	$814.12		$877.8594	$877.86	$877.90	$877.80