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	$241.72	12.540%	$272.0317	$272.03	$272.05	$272.00
Purchase #2	$74.44	5.426%	$78.4791	$78.48	$78.50	$78.50
Purchase #3	$211.77	9.595%	$232.0893	$232.09	$232.10	$232.10
Purchase #4	$53.90	10.209%	$59.4027	$59.40	$59.40	$59.40
Purchase #5	$52.97	12.432%	$59.5552	$59.56	$59.55	$59.60
Purchase #6	$164.63	3.215%	$169.9229	$169.92	$169.90	$169.90
Purchase #7	$112.66	5.663%	$119.0399	$119.04	$119.05	$119.00
7 purchase totals =	$912.09		$990.5208	$990.52	$990.55	$990.50