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	$131.68	9.800%	$144.5846	$144.58	$144.60	$144.60
Purchase #2	$55.46	13.350%	$62.8639	$62.86	$62.85	$62.90
Purchase #3	$137.84	4.157%	$143.57	$143.57	$143.55	$143.60
Purchase #4	$39.78	11.465%	$44.3408	$44.34	$44.35	$44.30
Purchase #5	$72.96	9.628%	$79.9846	$79.98	$80.00	$80.00
Purchase #6	$228.81	13.592%	$259.9099	$259.91	$259.90	$259.90
Purchase #7	$208.53	9.144%	$227.598	$227.60	$227.60	$227.60
7 purchase totals =	$875.06		$962.8518	$962.84	$962.85	$962.90