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	$74.98	6.635%	$79.9549	$79.95	$79.95	$80.00
Purchase #2	$117.94	7.273%	$126.5178	$126.52	$126.50	$126.50
Purchase #3	$102.34	10.827%	$113.4204	$113.42	$113.40	$113.40
Purchase #4	$52.85	11.732%	$59.0504	$59.05	$59.05	$59.10
Purchase #5	$81.96	10.442%	$90.5183	$90.52	$90.50	$90.50
Purchase #6	$62.45	11.153%	$69.415	$69.42	$69.40	$69.40
Purchase #7	$115.99	8.533%	$125.8874	$125.89	$125.90	$125.90
7 purchase totals =	$608.51		$664.7642	$664.77	$664.70	$664.80