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	$93.54	12.750%	$105.4664	$105.47	$105.45	$105.50
Purchase #2	$34.80	12.706%	$39.2217	$39.22	$39.20	$39.20
Purchase #3	$42.85	5.686%	$45.2865	$45.29	$45.30	$45.30
Purchase #4	$160.59	9.265%	$175.4687	$175.47	$175.45	$175.50
Purchase #5	$139.96	10.684%	$154.9133	$154.91	$154.90	$154.90
Purchase #6	$103.52	8.662%	$112.4869	$112.49	$112.50	$112.50
Purchase #7	$39.84	11.523%	$44.4308	$44.43	$44.45	$44.40
7 purchase totals =	$615.10		$677.2743	$677.28	$677.25	$677.30