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	$37.66	4.572%	$39.3818	$39.38	$39.40	$39.40
Purchase #2	$17.63	6.817%	$18.8318	$18.83	$18.85	$18.80
Purchase #3	$247.59	12.186%	$277.7613	$277.76	$277.75	$277.80
Purchase #4	$134.72	3.404%	$139.3059	$139.31	$139.30	$139.30
Purchase #5	$156.80	6.464%	$166.9356	$166.94	$166.95	$166.90
Purchase #6	$97.53	3.222%	$100.6724	$100.67	$100.65	$100.70
Purchase #7	$21.85	3.527%	$22.6206	$22.62	$22.60	$22.60
7 purchase totals =	$713.78		$765.5094	$765.51	$765.50	$765.50