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	$46.58	11.377%	$51.8794	$51.88	$51.90	$51.90
Purchase #2	$92.79	13.572%	$105.3835	$105.38	$105.40	$105.40
Purchase #3	$157.68	4.625%	$164.9727	$164.97	$164.95	$165.00
Purchase #4	$105.38	6.372%	$112.0948	$112.09	$112.10	$112.10
Purchase #5	$39.60	8.364%	$42.9121	$42.91	$42.90	$42.90
Purchase #6	$71.85	11.390%	$80.0337	$80.03	$80.05	$80.00
Purchase #7	$129.60	3.114%	$133.6357	$133.64	$133.65	$133.60
7 purchase totals =	$643.48		$690.9119	$690.90	$690.95	$690.90