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	$65.59	10.469%	$72.4566	$72.46	$72.45	$72.50
Purchase #2	$215.71	5.190%	$226.9053	$226.91	$226.90	$226.90
Purchase #3	$229.51	9.379%	$251.0357	$251.04	$251.05	$251.00
Purchase #4	$94.35	9.690%	$103.4925	$103.49	$103.50	$103.50
Purchase #5	$38.57	4.652%	$40.3643	$40.36	$40.35	$40.40
Purchase #6	$180.55	10.693%	$199.8562	$199.86	$199.85	$199.90
Purchase #7	$28.58	3.859%	$29.6829	$29.68	$29.70	$29.70
7 purchase totals =	$852.86		$923.7935	$923.80	$923.80	$923.90