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	$239.81	8.577%	$260.3785	$260.38	$260.40	$260.40
Purchase #2	$37.65	10.215%	$41.4959	$41.50	$41.50	$41.50
Purchase #3	$167.85	12.755%	$189.2593	$189.26	$189.25	$189.30
Purchase #4	$11.96	9.392%	$13.0833	$13.08	$13.10	$13.10
Purchase #5	$96.59	7.843%	$104.1656	$104.17	$104.15	$104.20
Purchase #6	$6.36	11.507%	$7.0918	$7.09	$7.10	$7.10
Purchase #7	$116.82	5.584%	$123.3432	$123.34	$123.35	$123.30
7 purchase totals =	$677.04		$738.8176	$738.82	$738.85	$738.90