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	$139.91	3.238%	$144.4403	$144.44	$144.45	$144.40
Purchase #2	$116.44	10.496%	$128.6615	$128.66	$128.65	$128.70
Purchase #3	$247.41	12.694%	$278.8162	$278.82	$278.80	$278.80
Purchase #4	$188.46	13.418%	$213.7476	$213.75	$213.75	$213.70
Purchase #5	$60.57	3.218%	$62.5191	$62.52	$62.50	$62.50
Purchase #6	$47.51	8.185%	$51.3987	$51.40	$51.40	$51.40
Purchase #7	$93.34	6.405%	$99.3184	$99.32	$99.30	$99.30
7 purchase totals =	$893.64		$978.9018	$978.91	$978.85	$978.80