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	$79.85	3.718%	$82.8188	$82.82	$82.80	$82.80
Purchase #2	$170.72	5.268%	$179.7135	$179.71	$179.70	$179.70
Purchase #3	$100.46	13.250%	$113.771	$113.77	$113.75	$113.80
Purchase #4	$230.67	13.242%	$261.2153	$261.22	$261.20	$261.20
Purchase #5	$86.76	9.296%	$94.8252	$94.83	$94.85	$94.80
Purchase #6	$186.55	3.308%	$192.7211	$192.72	$192.70	$192.70
Purchase #7	$136.99	10.550%	$151.4424	$151.44	$151.45	$151.40
7 purchase totals =	$992.00		$1,076.5073	$1,076.51	$1,076.45	$1,076.40