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	$192.54	13.680%	$218.8795	$218.88	$218.90	$218.90
Purchase #2	$130.38	6.712%	$139.1311	$139.13	$139.15	$139.10
Purchase #3	$80.54	11.622%	$89.9004	$89.90	$89.90	$89.90
Purchase #4	$99.71	12.215%	$111.8896	$111.89	$111.90	$111.90
Purchase #5	$128.41	8.638%	$139.5021	$139.50	$139.50	$139.50
Purchase #6	$154.65	7.452%	$166.1745	$166.17	$166.15	$166.20
Purchase #7	$22.43	9.787%	$24.6252	$24.63	$24.65	$24.60
7 purchase totals =	$808.66		$890.1024	$890.10	$890.15	$890.10