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	$84.57	7.541%	$90.9474	$90.95	$90.95	$90.90
Purchase #2	$46.78	8.667%	$50.8344	$50.83	$50.85	$50.80
Purchase #3	$38.60	4.498%	$40.3362	$40.34	$40.35	$40.30
Purchase #4	$135.35	13.347%	$153.4152	$153.42	$153.40	$153.40
Purchase #5	$58.96	10.832%	$65.3465	$65.35	$65.35	$65.30
Purchase #6	$38.59	12.653%	$43.4728	$43.47	$43.45	$43.50
Purchase #7	$134.71	6.238%	$143.1132	$143.11	$143.10	$143.10
7 purchase totals =	$537.56		$587.4657	$587.47	$587.45	$587.30