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	$246.63	13.758%	$280.5614	$280.56	$280.55	$280.60
Purchase #2	$38.39	12.267%	$43.0993	$43.10	$43.10	$43.10
Purchase #3	$204.26	3.481%	$211.3703	$211.37	$211.35	$211.40
Purchase #4	$19.46	10.308%	$21.4659	$21.47	$21.45	$21.50
Purchase #5	$109.40	6.558%	$116.5745	$116.57	$116.55	$116.60
Purchase #6	$44.42	13.455%	$50.3967	$50.40	$50.40	$50.40
Purchase #7	$72.36	11.511%	$80.6894	$80.69	$80.70	$80.70
7 purchase totals =	$734.92		$804.1575	$804.16	$804.10	$804.30