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	$18.93	13.768%	$21.5363	$21.54	$21.55	$21.50
Purchase #2	$143.55	3.460%	$148.5168	$148.52	$148.50	$148.50
Purchase #3	$203.47	9.168%	$222.1241	$222.12	$222.10	$222.10
Purchase #4	$225.61	5.515%	$238.0524	$238.05	$238.05	$238.10
Purchase #5	$72.63	5.791%	$76.836	$76.84	$76.85	$76.80
Purchase #6	$34.45	10.196%	$37.9625	$37.96	$37.95	$38.00
Purchase #7	$249.80	12.106%	$280.0408	$280.04	$280.05	$280.00
7 purchase totals =	$948.44		$1,025.0689	$1,025.07	$1,025.05	$1,025.00