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	$72.50	13.810%	$82.5123	$82.51	$82.50	$82.50
Purchase #2	$27.80	4.665%	$29.0969	$29.10	$29.10	$29.10
Purchase #3	$238.34	10.429%	$263.1965	$263.20	$263.20	$263.20
Purchase #4	$94.36	11.750%	$105.4473	$105.45	$105.45	$105.40
Purchase #5	$163.28	9.684%	$179.092	$179.09	$179.10	$179.10
Purchase #6	$129.75	8.783%	$141.1459	$141.15	$141.15	$141.10
Purchase #7	$198.33	5.329%	$208.899	$208.90	$208.90	$208.90
7 purchase totals =	$924.36		$1,009.3899	$1,009.40	$1,009.40	$1,009.30