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	$116.39	12.570%	$131.0202	$131.02	$131.00	$131.00
Purchase #2	$128.66	7.629%	$138.4755	$138.48	$138.50	$138.50
Purchase #3	$38.80	9.578%	$42.5163	$42.52	$42.50	$42.50
Purchase #4	$13.59	13.499%	$15.4245	$15.42	$15.40	$15.40
Purchase #5	$239.71	12.275%	$269.1344	$269.13	$269.15	$269.10
Purchase #6	$248.92	10.317%	$274.6011	$274.60	$274.60	$274.60
Purchase #7	$183.48	9.440%	$200.8005	$200.80	$200.80	$200.80
7 purchase totals =	$969.55		$1,071.9725	$1,071.97	$1,071.95	$1,071.90