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	$25.58	13.304%	$28.9832	$28.98	$29.00	$29.00
Purchase #2	$154.75	6.369%	$164.606	$164.61	$164.60	$164.60
Purchase #3	$104.64	10.593%	$115.7245	$115.72	$115.70	$115.70
Purchase #4	$38.49	9.119%	$41.9999	$42.00	$42.00	$42.00
Purchase #5	$51.63	3.781%	$53.5821	$53.58	$53.60	$53.60
Purchase #6	$137.82	9.282%	$150.6125	$150.61	$150.60	$150.60
Purchase #7	$51.58	13.436%	$58.5103	$58.51	$58.50	$58.50
7 purchase totals =	$564.49		$614.0185	$614.01	$614.00	$614.00