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	$225.47	13.381%	$255.6401	$255.64	$255.65	$255.60
Purchase #2	$59.40	9.817%	$65.2313	$65.23	$65.25	$65.20
Purchase #3	$200.47	7.489%	$215.4832	$215.48	$215.50	$215.50
Purchase #4	$212.64	12.336%	$238.8713	$238.87	$238.85	$238.90
Purchase #5	$248.27	13.168%	$280.9622	$280.96	$280.95	$281.00
Purchase #6	$20.97	5.483%	$22.1198	$22.12	$22.10	$22.10
Purchase #7	$46.71	6.399%	$49.699	$49.70	$49.70	$49.70
7 purchase totals =	$1,013.93		$1,128.0069	$1,128.00	$1,128.00	$1,128.00