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	$35.70	13.608%	$40.5581	$40.56	$40.55	$40.60
Purchase #2	$223.56	3.351%	$231.0515	$231.05	$231.05	$231.10
Purchase #3	$199.72	11.531%	$222.7497	$222.75	$222.75	$222.70
Purchase #4	$246.69	13.796%	$280.7234	$280.72	$280.70	$280.70
Purchase #5	$189.98	3.673%	$196.958	$196.96	$196.95	$197.00
Purchase #6	$29.31	11.491%	$32.678	$32.68	$32.70	$32.70
Purchase #7	$76.86	13.797%	$87.4644	$87.46	$87.45	$87.50
7 purchase totals =	$1,001.82		$1,092.1831	$1,092.18	$1,092.15	$1,092.30