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	$220.46	8.238%	$238.6215	$238.62	$238.60	$238.60
Purchase #2	$119.91	6.543%	$127.7557	$127.76	$127.75	$127.80
Purchase #3	$204.30	10.600%	$225.9558	$225.96	$225.95	$226.00
Purchase #4	$182.59	7.441%	$196.1765	$196.18	$196.20	$196.20
Purchase #5	$241.65	4.753%	$253.1356	$253.14	$253.15	$253.10
Purchase #6	$98.87	12.423%	$111.1526	$111.15	$111.15	$111.20
Purchase #7	$206.46	12.250%	$231.7514	$231.75	$231.75	$231.80
7 purchase totals =	$1,274.24		$1,384.5491	$1,384.56	$1,384.55	$1,384.70