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	$160.44	3.478%	$166.0201	$166.02	$166.00	$166.00
Purchase #2	$56.84	4.448%	$59.3682	$59.37	$59.35	$59.40
Purchase #3	$59.93	10.508%	$66.2274	$66.23	$66.25	$66.20
Purchase #4	$42.98	8.516%	$46.6402	$46.64	$46.65	$46.60
Purchase #5	$157.90	8.857%	$171.8852	$171.89	$171.90	$171.90
Purchase #6	$114.40	6.278%	$121.582	$121.58	$121.60	$121.60
Purchase #7	$208.35	5.340%	$219.4759	$219.48	$219.50	$219.50
7 purchase totals =	$800.84		$851.1990	$851.21	$851.25	$851.20