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	$204.83	3.196%	$211.3764	$211.38	$211.40	$211.40
Purchase #2	$128.83	7.435%	$138.4085	$138.41	$138.40	$138.40
Purchase #3	$60.84	10.826%	$67.4265	$67.43	$67.45	$67.40
Purchase #4	$34.28	8.466%	$37.1821	$37.18	$37.20	$37.20
Purchase #5	$76.57	3.706%	$79.4077	$79.41	$79.40	$79.40
Purchase #6	$130.51	9.627%	$143.0742	$143.07	$143.05	$143.10
Purchase #7	$213.50	4.362%	$222.8129	$222.81	$222.80	$222.80
7 purchase totals =	$849.36		$899.6883	$899.69	$899.70	$899.70