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	$39.50	9.153%	$43.1154	$43.12	$43.10	$43.10
Purchase #2	$33.39	13.791%	$37.9948	$37.99	$38.00	$38.00
Purchase #3	$31.81	11.786%	$35.5591	$35.56	$35.55	$35.60
Purchase #4	$195.79	6.689%	$208.8864	$208.89	$208.90	$208.90
Purchase #5	$246.59	5.174%	$259.3486	$259.35	$259.35	$259.30
Purchase #6	$110.80	7.469%	$119.0757	$119.08	$119.10	$119.10
Purchase #7	$142.81	9.344%	$156.1542	$156.15	$156.15	$156.20
7 purchase totals =	$800.69		$860.1342	$860.14	$860.15	$860.20