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	$113.55	12.645%	$127.9084	$127.91	$127.90	$127.90
Purchase #2	$103.42	10.327%	$114.1002	$114.10	$114.10	$114.10
Purchase #3	$86.73	10.702%	$96.0118	$96.01	$96.00	$96.00
Purchase #4	$244.74	12.452%	$275.215	$275.22	$275.20	$275.20
Purchase #5	$117.77	3.102%	$121.4232	$121.42	$121.40	$121.40
Purchase #6	$81.30	10.538%	$89.8674	$89.87	$89.85	$89.90
Purchase #7	$218.50	10.298%	$241.0011	$241.00	$241.00	$241.00
7 purchase totals =	$966.01		$1,065.5271	$1,065.53	$1,065.45	$1,065.50