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	$214.61	12.769%	$242.0136	$242.01	$242.00	$242.00
Purchase #2	$25.96	7.308%	$27.8572	$27.86	$27.85	$27.90
Purchase #3	$126.85	3.635%	$131.461	$131.46	$131.45	$131.50
Purchase #4	$177.77	9.770%	$195.1381	$195.14	$195.15	$195.10
Purchase #5	$178.66	3.231%	$184.4325	$184.43	$184.45	$184.40
Purchase #6	$71.65	8.549%	$77.7754	$77.78	$77.80	$77.80
Purchase #7	$76.56	8.665%	$83.1939	$83.19	$83.20	$83.20
7 purchase totals =	$872.06		$941.8717	$941.87	$941.90	$941.90