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	$36.25	9.505%	$39.6956	$39.70	$39.70	$39.70
Purchase #2	$33.62	10.354%	$37.101	$37.10	$37.10	$37.10
Purchase #3	$108.86	10.568%	$120.3643	$120.36	$120.35	$120.40
Purchase #4	$204.69	6.407%	$217.8045	$217.80	$217.80	$217.80
Purchase #5	$53.55	11.647%	$59.787	$59.79	$59.80	$59.80
Purchase #6	$13.82	12.110%	$15.4936	$15.49	$15.50	$15.50
Purchase #7	$7.71	6.175%	$8.1861	$8.19	$8.20	$8.20
7 purchase totals =	$458.50		$498.4321	$498.43	$498.45	$498.50