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	$35.47	8.721%	$38.5633	$38.56	$38.55	$38.60
Purchase #2	$135.29	5.416%	$142.6173	$142.62	$142.60	$142.60
Purchase #3	$56.90	7.597%	$61.2227	$61.22	$61.20	$61.20
Purchase #4	$233.48	6.762%	$249.2679	$249.27	$249.25	$249.30
Purchase #5	$206.53	9.473%	$226.0946	$226.09	$226.10	$226.10
Purchase #6	$58.46	6.354%	$62.1745	$62.17	$62.15	$62.20
Purchase #7	$52.97	12.194%	$59.4292	$59.43	$59.45	$59.40
7 purchase totals =	$779.10		$839.3695	$839.36	$839.30	$839.40