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	$123.54	6.201%	$131.2007	$131.20	$131.20	$131.20
Purchase #2	$250.37	13.186%	$283.3838	$283.38	$283.40	$283.40
Purchase #3	$105.84	3.682%	$109.737	$109.74	$109.75	$109.70
Purchase #4	$12.79	11.856%	$14.3064	$14.31	$14.30	$14.30
Purchase #5	$74.93	10.815%	$83.0337	$83.03	$83.05	$83.00
Purchase #6	$99.80	5.482%	$105.271	$105.27	$105.25	$105.30
Purchase #7	$66.40	4.652%	$69.4889	$69.49	$69.50	$69.50
7 purchase totals =	$733.67		$796.4215	$796.42	$796.45	$796.40