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	$38.65	13.553%	$43.8882	$43.89	$43.90	$43.90
Purchase #2	$103.44	12.421%	$116.2883	$116.29	$116.30	$116.30
Purchase #3	$45.54	12.825%	$51.3805	$51.38	$51.40	$51.40
Purchase #4	$66.49	10.223%	$73.2873	$73.29	$73.30	$73.30
Purchase #5	$39.86	8.253%	$43.1496	$43.15	$43.15	$43.10
Purchase #6	$69.62	9.334%	$76.1183	$76.12	$76.10	$76.10
Purchase #7	$244.45	5.599%	$258.1368	$258.14	$258.15	$258.10
7 purchase totals =	$608.05		$662.2490	$662.26	$662.30	$662.20