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	$104.58	11.606%	$116.7176	$116.72	$116.70	$116.70
Purchase #2	$141.52	5.244%	$148.9413	$148.94	$148.95	$148.90
Purchase #3	$59.65	9.762%	$65.473	$65.47	$65.45	$65.50
Purchase #4	$70.27	3.637%	$72.8257	$72.83	$72.85	$72.80
Purchase #5	$125.26	13.669%	$142.3818	$142.38	$142.40	$142.40
Purchase #6	$28.28	11.194%	$31.4457	$31.45	$31.45	$31.40
Purchase #7	$248.39	13.103%	$280.9365	$280.94	$280.95	$280.90
7 purchase totals =	$777.95		$858.7216	$858.73	$858.75	$858.60