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	$207.90	9.455%	$227.5569	$227.56	$227.55	$227.60
Purchase #2	$233.61	12.700%	$263.2785	$263.28	$263.30	$263.30
Purchase #3	$46.60	10.771%	$51.6193	$51.62	$51.60	$51.60
Purchase #4	$215.79	10.660%	$238.7932	$238.79	$238.80	$238.80
Purchase #5	$66.35	3.693%	$68.8003	$68.80	$68.80	$68.80
Purchase #6	$82.61	8.677%	$89.7781	$89.78	$89.80	$89.80
Purchase #7	$90.69	9.113%	$98.9546	$98.95	$98.95	$99.00
7 purchase totals =	$943.55		$1,038.7809	$1,038.78	$1,038.80	$1,038.90