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	$38.57	3.812%	$40.0403	$40.04	$40.05	$40.00
Purchase #2	$51.54	11.570%	$57.5032	$57.50	$57.50	$57.50
Purchase #3	$66.98	6.806%	$71.5387	$71.54	$71.55	$71.50
Purchase #4	$35.65	6.410%	$37.9352	$37.94	$37.95	$37.90
Purchase #5	$237.62	13.262%	$269.1332	$269.13	$269.15	$269.10
Purchase #6	$140.86	9.364%	$154.0501	$154.05	$154.05	$154.10
Purchase #7	$104.26	11.516%	$116.2666	$116.27	$116.25	$116.30
7 purchase totals =	$675.48		$746.4673	$746.47	$746.50	$746.40