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	$82.87	9.577%	$90.8065	$90.81	$90.80	$90.80
Purchase #2	$94.27	10.160%	$103.8478	$103.85	$103.85	$103.80
Purchase #3	$218.55	10.157%	$240.7481	$240.75	$240.75	$240.70
Purchase #4	$43.87	10.575%	$48.5093	$48.51	$48.50	$48.50
Purchase #5	$141.47	7.235%	$151.7054	$151.71	$151.70	$151.70
Purchase #6	$168.91	8.736%	$183.666	$183.67	$183.65	$183.70
Purchase #7	$228.29	4.134%	$237.7275	$237.73	$237.75	$237.70
7 purchase totals =	$978.23		$1,057.0106	$1,057.03	$1,057.00	$1,056.90