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	$76.83	5.784%	$81.2738	$81.27	$81.25	$81.30
Purchase #2	$129.64	9.687%	$142.1982	$142.20	$142.20	$142.20
Purchase #3	$108.86	13.650%	$123.7194	$123.72	$123.70	$123.70
Purchase #4	$119.68	10.737%	$132.53	$132.53	$132.55	$132.50
Purchase #5	$62.62	13.830%	$71.2803	$71.28	$71.30	$71.30
Purchase #6	$50.48	11.357%	$56.213	$56.21	$56.20	$56.20
Purchase #7	$64.96	9.636%	$71.2195	$71.22	$71.20	$71.20
7 purchase totals =	$613.07		$678.4342	$678.43	$678.40	$678.40