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	$248.29	12.798%	$280.0662	$280.07	$280.05	$280.10
Purchase #2	$139.30	3.504%	$144.1811	$144.18	$144.20	$144.20
Purchase #3	$111.87	12.241%	$125.564	$125.56	$125.55	$125.60
Purchase #4	$183.38	10.328%	$202.3195	$202.32	$202.30	$202.30
Purchase #5	$189.69	12.871%	$214.105	$214.11	$214.10	$214.10
Purchase #6	$5.76	5.515%	$6.0777	$6.08	$6.10	$6.10
Purchase #7	$82.83	8.243%	$89.6577	$89.66	$89.65	$89.70
7 purchase totals =	$961.12		$1,061.9712	$1,061.98	$1,061.95	$1,062.10