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	$148.48	13.160%	$168.02	$168.02	$168.00	$168.00
Purchase #2	$138.78	12.808%	$156.5549	$156.55	$156.55	$156.60
Purchase #3	$5.51	11.461%	$6.1415	$6.14	$6.15	$6.10
Purchase #4	$134.89	3.471%	$139.572	$139.57	$139.55	$139.60
Purchase #5	$131.67	12.874%	$148.6212	$148.62	$148.60	$148.60
Purchase #6	$67.76	13.466%	$76.8846	$76.88	$76.90	$76.90
Purchase #7	$22.38	9.154%	$24.4287	$24.43	$24.45	$24.40
7 purchase totals =	$649.47		$720.2229	$720.21	$720.20	$720.20