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	$29.97	6.281%	$31.8524	$31.85	$31.85	$31.90
Purchase #2	$113.64	5.455%	$119.8391	$119.84	$119.85	$119.80
Purchase #3	$198.94	11.505%	$221.828	$221.83	$221.85	$221.80
Purchase #4	$97.35	7.132%	$104.293	$104.29	$104.30	$104.30
Purchase #5	$100.28	10.833%	$111.1433	$111.14	$111.15	$111.10
Purchase #6	$57.51	3.803%	$59.6971	$59.70	$59.70	$59.70
Purchase #7	$132.90	6.626%	$141.706	$141.71	$141.70	$141.70
7 purchase totals =	$730.59		$790.3589	$790.36	$790.40	$790.30