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	$38.96	3.501%	$40.324	$40.32	$40.30	$40.30
Purchase #2	$145.62	7.196%	$156.0988	$156.10	$156.10	$156.10
Purchase #3	$206.87	11.680%	$231.0324	$231.03	$231.05	$231.00
Purchase #4	$132.40	12.202%	$148.5554	$148.56	$148.55	$148.60
Purchase #5	$248.78	12.846%	$280.7383	$280.74	$280.75	$280.70
Purchase #6	$97.27	8.434%	$105.4738	$105.47	$105.45	$105.50
Purchase #7	$135.58	8.349%	$146.8996	$146.90	$146.90	$146.90
7 purchase totals =	$1,005.48		$1,109.1223	$1,109.12	$1,109.10	$1,109.10