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	$82.56	8.266%	$89.3844	$89.38	$89.40	$89.40
Purchase #2	$239.58	10.116%	$263.8159	$263.82	$263.80	$263.80
Purchase #3	$46.85	4.714%	$49.0585	$49.06	$49.05	$49.10
Purchase #4	$127.79	7.870%	$137.8471	$137.85	$137.85	$137.80
Purchase #5	$33.83	13.622%	$38.4383	$38.44	$38.45	$38.40
Purchase #6	$186.45	4.822%	$195.4406	$195.44	$195.45	$195.40
Purchase #7	$223.77	3.347%	$231.2596	$231.26	$231.25	$231.30
7 purchase totals =	$940.83		$1,005.2444	$1,005.25	$1,005.25	$1,005.20