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	$16.89	5.864%	$17.8804	$17.88	$17.90	$17.90
Purchase #2	$26.92	9.597%	$29.5035	$29.50	$29.50	$29.50
Purchase #3	$145.45	11.690%	$162.4531	$162.45	$162.45	$162.50
Purchase #4	$36.60	11.366%	$40.76	$40.76	$40.75	$40.80
Purchase #5	$164.86	10.392%	$181.9923	$181.99	$182.00	$182.00
Purchase #6	$95.33	3.449%	$98.6179	$98.62	$98.60	$98.60
Purchase #7	$71.27	9.755%	$78.2224	$78.22	$78.20	$78.20
7 purchase totals =	$557.32		$609.4296	$609.42	$609.40	$609.50