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	$248.58	9.578%	$272.389	$272.39	$272.40	$272.40
Purchase #2	$136.40	8.341%	$147.7771	$147.78	$147.80	$147.80
Purchase #3	$99.80	9.527%	$109.3079	$109.31	$109.30	$109.30
Purchase #4	$236.83	10.662%	$262.0808	$262.08	$262.10	$262.10
Purchase #5	$118.47	8.739%	$128.8231	$128.82	$128.80	$128.80
Purchase #6	$158.53	12.570%	$178.4572	$178.46	$178.45	$178.50
Purchase #7	$77.71	5.442%	$81.939	$81.94	$81.95	$81.90
7 purchase totals =	$1,076.32		$1,180.7741	$1,180.78	$1,180.80	$1,180.80