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	$70.76	9.658%	$77.594	$77.59	$77.60	$77.60
Purchase #2	$203.78	8.495%	$221.0911	$221.09	$221.10	$221.10
Purchase #3	$181.41	13.552%	$205.9947	$205.99	$206.00	$206.00
Purchase #4	$24.59	12.422%	$27.6446	$27.64	$27.65	$27.60
Purchase #5	$96.60	10.369%	$106.6165	$106.62	$106.60	$106.60
Purchase #6	$247.49	13.509%	$280.9234	$280.92	$280.90	$280.90
Purchase #7	$90.27	8.646%	$98.0747	$98.07	$98.05	$98.10
7 purchase totals =	$914.90		$1,017.9390	$1,017.92	$1,017.90	$1,017.90