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	$236.59	13.463%	$268.4421	$268.44	$268.45	$268.40
Purchase #2	$184.90	13.623%	$210.0889	$210.09	$210.10	$210.10
Purchase #3	$102.42	13.149%	$115.8872	$115.89	$115.90	$115.90
Purchase #4	$248.50	12.464%	$279.473	$279.47	$279.45	$279.50
Purchase #5	$94.65	9.702%	$103.8329	$103.83	$103.85	$103.80
Purchase #6	$123.36	13.386%	$139.873	$139.87	$139.85	$139.90
Purchase #7	$68.30	4.806%	$71.5825	$71.58	$71.60	$71.60
7 purchase totals =	$1,058.72		$1,189.1796	$1,189.17	$1,189.20	$1,189.20