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	$94.42	6.587%	$100.6394	$100.64	$100.65	$100.60
Purchase #2	$136.51	6.726%	$145.6917	$145.69	$145.70	$145.70
Purchase #3	$75.59	7.639%	$81.3643	$81.36	$81.35	$81.40
Purchase #4	$121.28	13.216%	$137.3084	$137.31	$137.30	$137.30
Purchase #5	$199.75	11.559%	$222.8391	$222.84	$222.85	$222.80
Purchase #6	$39.92	10.605%	$44.1535	$44.15	$44.15	$44.20
Purchase #7	$55.25	11.215%	$61.4463	$61.45	$61.45	$61.40
7 purchase totals =	$722.72		$793.4427	$793.44	$793.45	$793.40