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	$37.38	4.440%	$39.0397	$39.04	$39.05	$39.00
Purchase #2	$25.42	8.502%	$27.5812	$27.58	$27.60	$27.60
Purchase #3	$103.69	5.302%	$109.1876	$109.19	$109.20	$109.20
Purchase #4	$93.87	12.533%	$105.6347	$105.63	$105.65	$105.60
Purchase #5	$89.62	11.340%	$99.7829	$99.78	$99.80	$99.80
Purchase #6	$206.50	5.326%	$217.4982	$217.50	$217.50	$217.50
Purchase #7	$169.75	7.132%	$181.8566	$181.86	$181.85	$181.90
7 purchase totals =	$726.23		$780.5809	$780.58	$780.65	$780.60