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	$69.81	4.315%	$72.8223	$72.82	$72.80	$72.80
Purchase #2	$122.32	8.190%	$132.338	$132.34	$132.35	$132.30
Purchase #3	$198.74	8.567%	$215.7661	$215.77	$215.75	$215.80
Purchase #4	$140.40	5.570%	$148.2203	$148.22	$148.20	$148.20
Purchase #5	$81.94	11.847%	$91.6474	$91.65	$91.65	$91.60
Purchase #6	$40.78	4.343%	$42.5511	$42.55	$42.55	$42.60
Purchase #7	$250.45	11.829%	$280.0757	$280.08	$280.10	$280.10
7 purchase totals =	$904.44		$983.4209	$983.43	$983.40	$983.40