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	$66.31	8.270%	$71.7938	$71.79	$71.80	$71.80
Purchase #2	$189.92	4.377%	$198.2328	$198.23	$198.25	$198.20
Purchase #3	$39.89	8.312%	$43.2057	$43.21	$43.20	$43.20
Purchase #4	$24.41	11.143%	$27.13	$27.13	$27.15	$27.10
Purchase #5	$140.93	5.268%	$148.3542	$148.35	$148.35	$148.40
Purchase #6	$112.31	13.682%	$127.6763	$127.68	$127.70	$127.70
Purchase #7	$23.71	5.846%	$25.0961	$25.10	$25.10	$25.10
7 purchase totals =	$597.48		$641.4889	$641.49	$641.55	$641.50