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	$6.99	12.681%	$7.8764	$7.88	$7.90	$7.90
Purchase #2	$163.98	9.566%	$179.6663	$179.67	$179.65	$179.70
Purchase #3	$38.77	6.310%	$41.2164	$41.22	$41.20	$41.20
Purchase #4	$52.37	5.299%	$55.1451	$55.15	$55.15	$55.10
Purchase #5	$82.47	10.254%	$90.9265	$90.93	$90.95	$90.90
Purchase #6	$86.98	4.247%	$90.674	$90.67	$90.65	$90.70
Purchase #7	$92.28	5.213%	$97.0906	$97.09	$97.10	$97.10
7 purchase totals =	$523.84		$562.5953	$562.61	$562.60	$562.60