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	$38.33	13.235%	$43.403	$43.40	$43.40	$43.40
Purchase #2	$88.82	3.498%	$91.9269	$91.93	$91.95	$91.90
Purchase #3	$118.88	10.580%	$131.4575	$131.46	$131.45	$131.50
Purchase #4	$48.82	3.347%	$50.454	$50.45	$50.45	$50.50
Purchase #5	$200.45	6.566%	$213.6115	$213.61	$213.60	$213.60
Purchase #6	$18.82	12.527%	$21.1776	$21.18	$21.20	$21.20
Purchase #7	$83.96	8.780%	$91.3317	$91.33	$91.35	$91.30
7 purchase totals =	$598.08		$643.3622	$643.36	$643.40	$643.40