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	$215.45	12.341%	$242.0387	$242.04	$242.05	$242.00
Purchase #2	$112.59	5.653%	$118.9547	$118.95	$118.95	$119.00
Purchase #3	$37.57	4.608%	$39.3012	$39.30	$39.30	$39.30
Purchase #4	$126.93	13.396%	$143.9335	$143.93	$143.95	$143.90
Purchase #5	$171.80	7.766%	$185.142	$185.14	$185.15	$185.10
Purchase #6	$98.82	10.539%	$109.2346	$109.23	$109.25	$109.20
Purchase #7	$98.43	10.463%	$108.7287	$108.73	$108.75	$108.70
7 purchase totals =	$861.59		$947.3334	$947.32	$947.40	$947.20