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	$77.79	4.206%	$81.0618	$81.06	$81.05	$81.10
Purchase #2	$181.73	10.266%	$200.3864	$200.39	$200.40	$200.40
Purchase #3	$27.77	5.854%	$29.3957	$29.40	$29.40	$29.40
Purchase #4	$9.73	7.651%	$10.4744	$10.47	$10.45	$10.50
Purchase #5	$85.47	13.654%	$97.1401	$97.14	$97.15	$97.10
Purchase #6	$133.82	5.766%	$141.5361	$141.54	$141.55	$141.50
Purchase #7	$76.45	3.157%	$78.8635	$78.86	$78.85	$78.90
7 purchase totals =	$592.76		$638.8580	$638.86	$638.85	$638.90