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	$198.96	9.801%	$218.4601	$218.46	$218.45	$218.50
Purchase #2	$238.54	10.298%	$263.1048	$263.10	$263.10	$263.10
Purchase #3	$195.78	11.372%	$218.0441	$218.04	$218.05	$218.00
Purchase #4	$134.59	10.564%	$148.8081	$148.81	$148.80	$148.80
Purchase #5	$13.33	13.626%	$15.1463	$15.15	$15.15	$15.10
Purchase #6	$86.93	7.547%	$93.4906	$93.49	$93.50	$93.50
Purchase #7	$45.27	13.652%	$51.4503	$51.45	$51.45	$51.50
7 purchase totals =	$913.40		$1,008.5043	$1,008.50	$1,008.50	$1,008.50