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	$27.54	8.407%	$29.8553	$29.86	$29.85	$29.90
Purchase #2	$176.69	3.741%	$183.3	$183.30	$183.30	$183.30
Purchase #3	$54.62	8.853%	$59.4555	$59.46	$59.45	$59.50
Purchase #4	$78.55	6.311%	$83.5073	$83.51	$83.50	$83.50
Purchase #5	$186.69	3.110%	$192.4961	$192.50	$192.50	$192.50
Purchase #6	$137.82	4.351%	$143.8165	$143.82	$143.80	$143.80
Purchase #7	$108.31	4.774%	$113.4807	$113.48	$113.50	$113.50
7 purchase totals =	$770.22		$805.9114	$805.93	$805.90	$806.00