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	$248.72	12.789%	$280.5288	$280.53	$280.55	$280.50
Purchase #2	$227.31	13.181%	$257.2717	$257.27	$257.25	$257.30
Purchase #3	$35.56	6.795%	$37.9763	$37.98	$38.00	$38.00
Purchase #4	$245.50	13.580%	$278.8389	$278.84	$278.85	$278.80
Purchase #5	$159.55	7.398%	$171.3535	$171.35	$171.35	$171.40
Purchase #6	$49.84	7.766%	$53.7106	$53.71	$53.70	$53.70
Purchase #7	$49.96	9.793%	$54.8526	$54.85	$54.85	$54.90
7 purchase totals =	$1,016.44		$1,134.5324	$1,134.53	$1,134.55	$1,134.60