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	$51.35	9.418%	$56.1861	$56.19	$56.20	$56.20
Purchase #2	$137.45	10.785%	$152.274	$152.27	$152.25	$152.30
Purchase #3	$67.83	6.119%	$71.9805	$71.98	$72.00	$72.00
Purchase #4	$19.53	7.647%	$21.0235	$21.02	$21.00	$21.00
Purchase #5	$203.89	3.860%	$211.7602	$211.76	$211.75	$211.80
Purchase #6	$93.30	13.407%	$105.8087	$105.81	$105.80	$105.80
Purchase #7	$250.89	11.829%	$280.5678	$280.57	$280.55	$280.60
7 purchase totals =	$824.24		$899.6008	$899.60	$899.55	$899.70