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	$166.59	9.841%	$182.9841	$182.98	$183.00	$183.00
Purchase #2	$82.98	10.533%	$91.7203	$91.72	$91.70	$91.70
Purchase #3	$36.88	8.172%	$39.8938	$39.89	$39.90	$39.90
Purchase #4	$50.81	5.491%	$53.6	$53.60	$53.60	$53.60
Purchase #5	$213.59	12.803%	$240.9359	$240.94	$240.95	$240.90
Purchase #6	$135.27	4.850%	$141.8306	$141.83	$141.85	$141.80
Purchase #7	$219.60	3.624%	$227.5583	$227.56	$227.55	$227.60
7 purchase totals =	$905.72		$978.5230	$978.52	$978.55	$978.50