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	$81.31	11.655%	$90.7867	$90.79	$90.80	$90.80
Purchase #2	$62.77	10.661%	$69.4619	$69.46	$69.45	$69.50
Purchase #3	$140.74	10.348%	$155.3038	$155.30	$155.30	$155.30
Purchase #4	$129.32	9.807%	$142.0024	$142.00	$142.00	$142.00
Purchase #5	$132.33	6.869%	$141.4197	$141.42	$141.40	$141.40
Purchase #6	$235.81	12.809%	$266.0149	$266.01	$266.00	$266.00
Purchase #7	$133.60	8.408%	$144.8331	$144.83	$144.85	$144.80
7 purchase totals =	$915.88		$1,009.8225	$1,009.81	$1,009.80	$1,009.80