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	$18.99	7.269%	$20.3704	$20.37	$20.35	$20.40
Purchase #2	$153.35	12.538%	$172.577	$172.58	$172.60	$172.60
Purchase #3	$220.42	8.108%	$238.2917	$238.29	$238.30	$238.30
Purchase #4	$152.96	4.169%	$159.3369	$159.34	$159.35	$159.30
Purchase #5	$56.91	10.479%	$62.8736	$62.87	$62.85	$62.90
Purchase #6	$59.96	13.747%	$68.2027	$68.20	$68.20	$68.20
Purchase #7	$189.95	3.650%	$196.8832	$196.88	$196.90	$196.90
7 purchase totals =	$852.54		$918.5355	$918.53	$918.55	$918.60